Help!

My betta has been scarily bloated for 3 days that I am aware of now. He is acting relatively normal, swimming normally, his fins look fine & he has appetite &doesn't seem to have discolorations or look paler yet anyway. He was spending a few days just hanging out in the corner of the tank an inch or 2 below the surface and was not coming over to say hi as usual 2days before this started. He had had a big bubble nest that was dissipating at that point so I thought he might just be a bit down plus I have been extra busy w an ongoing family emergency that has kept me from paying him very little attention. But truthfully I never did much but feed and change his water until I started learning about them. I have had him for 6 months & he was always building bubble nests so I went & got him a female the same day I noticed his belly. W my business The last 2 months have been very hard & I only changed his 3 gal tank water once a month the last 2 months. There is no heater cause I read you shouldn't put one on a tank that small so I just keep the heat in my apt up above 75. The heat was not wking for 2 different days & it got to 65 for a day each time most recently about 2 days before I saw his protruding belly. I have ruled out dropsy I think and swim bladder cause he's swimming normal. I thought it was constipation & fasted him for 2 days then gave him a quarter pea yesterday. I saw him poo a round opaque greenish tinted ball about the size of a pellet today & think it may have been the pea but not sure which leads me to think he's not constipated cause he's still swollen. There are no spots or wounds on him & I fed him 2 soaked pellets which is his only food cause I didn't know to vary food til this incident. Usually I give them to him dry & he got like 10 of them twice a day before!! Ugh I didn't know better cause he is a big betta & he eats up to 16 pellets in the 2 mins the directions say. Oh another reason I though I may have over fed him was cause I was so tired 5 or 6 days ago that I think I fed him twice for dinner. He is flattering at the new female in the separate tank next to his which I read is a good sign. I'm nervous to do the Epsom salt bath & cause him more stress. Also I did a 50% water change the day I noticed swelling and I did probably a 30% change today. There was a lot of poo on the bottom but no wasted food cause he's such a hungry hippo lol he raised out of the water to bite the pea off the spoon I was lowering the pea down w cause he was so hungry!!! I also tested the water at its worst and ammonia was right below bad and nitrate & nitrites were not optimal(can give exact amounts if important). One last variable I can think of is from day 1 when he used to live in a 1 gal tank I would give him 100% water change so maybe good bacteria never got to accumulate in his tank, could he have a bacterial infection?? His stomach is so stretched underneath which is visible from the side &not so visible from the top. Ok if an EXPERIENCED betta breeder preferably can offer advice please help I love him so and am just learning how to show him as I am new at this, so please no guilt trips from anyone cause I am doing the best I can under enormous pressure from unusual life circumstances. Him making me have more worries than my family emergency is enough of a lesson to learn to keep up w his maintenance better. Thank you )