Form and breathing advice needed

Hey, just started swimming again the past month after years of stopping. The getting back into the groove always sucks, i've been in this situation before quitting and rejoining the swim team (now just doing it for exercise). Basically back into the groove except my bad habits, which take months for me to fix, keep showing up. Mainly, it's that my stomach tends to droop with freestyle, somewhat during breaststroke but easier to fix, and sticks out with backstroke but is also easier to fix. I think it's fine during butterfly, probably because of using so much stomach muscle. It's kind of hereditary bad habit with many family members on my dad's side to arch our lower back constantly, do to our big butts. =P Anyway, i try fixing the problem but it wears me out in the water. Also for some reason i find it harder to take breaths. I could be tightening my abs too much...? All i remember from before was slowly fixing the problem until the correct way felt no different. It took months and sometimes i'd slip back into it, esp when tired. Has anyone else been through a similar problem and found a quick fix? Btw, my coach just yelled at me to keep my stomach up; now there is no one to yell at me so i'm looking for a more creative solution... always thinking i won't have to suffer to get results. There's just gotta be a loop hole- jus godda. Hope someone can help.