Couldn't keep my fasts

Im so in the trenches, for instance im a 17F this is the first time my Ramadan has gone so off-ish :( literally on the first 2-3 Ramadan i got sick (stomach issues) which still have been going on, and prior to that i have only kept 4 fast. I just feel anxious that idk how to fast because i have been suspecting gastritist which makes it worse if i keep a fast. My mom said i could keep the ones i missed in winters but that doesn't make me feel better, I just feel anxious as if im deceiving allah (nauzobillah) or not keeping them on purpose because im not "that ill". I heard theres no alternatives than keeping them or feeding miskeens. I just need some kind of reassurance/advice etc.