I'm in pain because I'm fat, I'm fat because I'm in pain

Ever since I went on anti depressants a few years ago, I have rapidly gained weight. I am not ashamed to say that I am a fat woman. People love to dance around the fact, saying I'm "curvy", "plus sized", etc. I'm just fat. I've been trying to lose weight as of late, watching what I eat, exercising, etc. I try not to overexert myself by doing too strenuous workouts, but I will go on walks, do yoga, or dance. Going on walks is tricky sometimes because I have a normally long labia that rubs against my underwear when I'm walking for too long. I'll try to wear pads or put aquafor down there but nothing really seems to work. My MAIN problem right now is that I must've pulled something at work the other day, because it is SO painful to bend both of my knees. I feel this stretchy ache in both of my thighs. I noticed it last night when I went to sit on the toilet, it hurt to sit down and I dreaded getting up because I knew it would hurt again. Painkillers aren't working and doing mundane things like climbing up steps or getting up from sitting hurts like hell. I want to tell my dad, who is a medical professional (not a doctor, but has experience) that I'm in pain to the point of tears. But he has been the most critical person of my weight gain and I know he will just make some snide comment about my size when I just need help with my legs in pain. I don't know what to do. I'm supposed to go to work tonight but I'm just in so much pain. I know I only brought this upon myself by being fat but I just want some way to relieve this pain.