I admire vegans, would be my ideal one day. Or even better, no need for "daily food" any more if I wish, one day.
I believe you a Theravada practitioner; if not, at least more aligned and accessing to Theravadin Pali Suttas. That's even more adored, for listening to compassionate heart and discernment than subscribing to words and preaching.
Likely the health issues you encountered not resulted from vegan meals, but the plant products are polluted, genetically modified, left them no longer having the same nutrients any more. If you read articles, the GMO soya bean contained 70% less nutrient (protein) than the original bean our grandpas eating. The soil polluted too, also pesticides and chemical fertilizers... you may read those articles about Monsanto, ADM, Bunge, Cargill and Dreyfus. Also, in ready-made vegan products like noodle, flour dough, bread... beancurd, are usually loaded with plasticizer, or GMO corn or GMO corn syrup giving volume or texture. It could result in nutrition imbalance. Better you add nuts, mushrooms, or some plant roots/fruits with great nutrients to your diet. The Chinese are very good with this eating for health knowledge, recorded in many Classical Texts of Chinese Medicine. Herbal plants such as types of Ginsengs, Angelicas (Dāngguī), wolfberries and Jujubes with great nutrients are commonly added in cooking to enhance health. However, possible some people with special body types not suitable to be vegans.
To my knowledge, every type of meat has it's equivalent in plant. Example, cashew nut = kidney (like in English kidney pie), chestnut = chicken meat, mushroom = meat (pork or beef, just flesh), walnut = fat of meat... So without meat, we human can still have the nutrient same as meat provided by plants.
If not, then for Chinese Mahayana, in Sutras I studied come to my understanding, that a lay-Buddhist can have the Three-Clean-Meat (三淨肉). That is the meat, a) not seen the killing, b) not heard the killing, c) not suspected the killing... not done for you in purpose. However, it seems this Three-Clean-Meat a Bhikkhu's meat in Theravada. Normally, buying ready prepared meat in the supermarket is OK. Although, lay-Buddhist the true Dharma follower not supposed to boast over the meat-eating, should take it as a necessary progression to the more ideal, i.e., being vegetarian. It's particularly disgraceful and condemned, if a Buddhist praised meat-eating, or encouraged other to eat meat. For those who taken the Bodhisattva vow, i.e., the Upāsakas (居士), then they should be vegetarian (unless health issue); so are the Bhiksus, unless they practicing Dhūta (頭陀行), i.e., going for alms round accepting what's given. These Dhūta-guna Bhiksus are normally Hinayana practitioners.
Some would like also some dislike, if I stated Theravada is not Hinayana. Hinayana practitioners are also one branch in Chinese Buddhism (which I admired, for their concentration on Dhyana with great Sutras teaching the practice, only in Chinese Canon). The great translator of Chinese Sutras Kumarajiva (344–413 CE) was a Hinayanist later turned Mahayanist, according to recorded documents. I think Kumarajiva had no idea what was Theravada though. Further, I don't find any equivalent records in the Five Vinayas of the Early 18 Buddhist Schools preserved in the Chinese Canon, that credited the Pali Vinaya of reporting the Buddha once eating meat offered by a general out of pity, another suspected meat eating offered by Uppalavannā the gift of 500 cow-robbers. If someone could enlighten me when the Pali Vinaya written and what the origin of it (such as to which early 18 Schools it related), would be a great interest to me. These are commonly used by some Theravadins (luckily not all) to credit meat eating, further contriving the ludicrous accusation of Mahayanist the Devadatta offshoot. Buddha condemned Devadatta advocating vegetarian only because Devadatta taken the Brahmin/heretic's doctrine that not eating meat granted one to be born in the Brahma world. This of course obviously was not Buddha Dharma. But one with fair mind would never mix up as that Buddha condemned vegetarianism.
For Tibetan Buddhism, the Tantric practice likely required meat eating, like in Ganacakra (eating Five Meats: human, horse, elephant, dog and beef), which a secret practice supposed not revealed to the public and uninitiated. It's understandable Dalai Lama will need to eat meat, for health reason; he is a Tantra Master, giving Kālacakra empowerment. Although not sure the Five Meats are still the same ingredients in Lamaism, or modernized? On the other hand, due to geographical condition, some people have to rely on meat as their main food source, I would assume Tibet is such place, also Mongolia. I heard that Khenpo Tsultrim Lodrö (who I like) and his Tibetan Buddhist School is revolutionizing for vegetarian practice.
I think I've given more than enough details, and fair accounts, on most of the arguments on vegetarianism of Buddhism, which I hope would be beneficial for the OP to make good choice, so are those who got the same doubts. Often fair accounts are not always liked.