Are my painful feelings, that I feel now, result of my past kamma
I think kamma is especially useful as an explanation of the present-and-future ... more so than of the past-and-present.
So "the present is the result of my past kamma" is less obviously helpful to me than, "present kamma -- i.e. present 'intentional action' -- affects the future".
Or is it something I am generating by doing something with free will in the present moment, that I am still not aware of that I can stop?
I found that a clear description of what causes "pain" are the four noble truths -- so pain or dukkha might be associated with some kind of "craving".
And there are many kinds of craving -- wanting to have things, wanting to keep things, having an idea about how things ought to be that isn't the way they are.
Another way to view that might be as "thinking too much" or as "inappropriate attention" -- I think the doctrine says, though, that the perception of something as being emotionally painful is a result of one's reaction to it and is not inherent in the thing itself.
Samana Johann's answer for example suggests you remain mindful of the breath instead, a practice called Anapanasati.
Because it seems like I have no way chance against painful feelings and they are controlling me
Buddhism might say that there isn't a "me". Sometimes there are pained feelings, sometimes there are non-pained feelings, in neither case is there a "me" which they're controlling. We might think there's a "me" but that "view" of "me" is likely just another clinging-to-an-idea of how-things-ought-to-be and therefore just another source of unhappiness (when the temporary present doesn't match the non-real ideal).
I read that Sankhara are subconscious tendencies. Is that the same as my feelings that keep me trapped?
There are a lot of different words in Buddhism. Some of them have broad meanings (more than one meaning), and of course different words are related.
The most thorough explanation of "sankhara" that I know is, Can anyone explain Sanskara / Sankara indepth?
Whereas "feelings" are one of the "five aggregates" i.e. skandhas.
Feelings (i.e. vedana) also appear in the description of the 12 nidanas.
And the word for "painfulness" might be dukkha.
Another word for "underlying tendency" might be anusaya.
The sense of feeling trapped might be a result of identifying -- "I" am trapped -- which is the subject of several doctrines and several practices (including a practice of generosity, considering others, and "taking refuge").