There are the 5 five hindrances that stand in the way as obstacles for developing in ones practice and for reaching Nibbana.
In brief the five hindrances are:
- Sensual Desire (kámacchanda)
- Aversion or Ill-will (vyápáda)
- Sleepiness – sloth (thina), torpor (middha), sluggishness
- Restlessness – worry about the future, regret of the past, anxiety (uddhacca-kukkucca)
- Doubt (skeptical doubt) (vicikicchá)
It could be no. 4, 5: worries or doubt about the practice that you are experiencing. If you practice under the Mahasi Sayadaw Tradition then the way to deal with such hindrances is to turn them into an object of observation, i.e. a meditation object and thereby making them a foundation for realizing insights. So when worry arises one can simply note it as "worried, worried" and if doubt arises one can note it as "doubting, doubting".
If one takes them as meditation objects then one will come to see that they also are subject to the 3 signs of existence; anicca, dukkha and anatta. One will come to see that all conditioned phenomena follows a standard formula which is: Arising, Presence, Dissolution. So when taken as meditation objects one will see that the worry or doubt arises, is present and then disappears. It might come again multiple times but the same procedure should be used every time, i.e. to observe and note them.
Here you can read more about The Five Hindrances and Their Conquest.
Also here is a great audio dhamma talk on the five hindrances by Ven. Bhikkhu Bodhi. Here is part 1 and part 2. This talk is highly recommended and i think it might be able to give you some answers. Ven. Bhikkhu Bodhi talks in depth about the hindrances and gives tools that can be used to overcome them.
Here is a great dhamma talk by Ven. Yuttadhammo that might just address your question. Its called Generating Motivation (Monk Radio). Here its talked about how one can generate motivation to practice.