I'm new and need help!!

Hi guys! So, I'm 25 years old and after having my rather large son at the age of 20 (he was 9lbs 3 oz) I have weight and fat that refuses to come off. Before I had him, I never had an issue with my figure. I was too skinny to most people. I could eat and eat, wore a size 0 and an XS shirt. I am 5'5" - 5'6" and used to weight 100-105 lbs. During my pregnancy I gained around 60 lbs. Which they kept telling me was "healthy" even though I KNEW it wasn't. Anyhow, my issue now is I weight roughtly 135-140 lbs, I can't lose any more weight. I've never been on a diet, and this past august I began training for my first half marathong ever. I completed TWO half marathons within one week of eachother, running without stopping! But, my problem is, MY GUT. Good lord its HUGE. I wear a 32 C bra, and I have very narrow hips, about 33-34" however my waist is 36-38" depending on when I measure it. Within the 6 months of running I truly only lost 3 lbs total. I don't know what to do to lose this fluffy, fat, unproportionate waist. I can't wear tight fitting clothes without looking or feeling pregnant. My legs are tiny, I still only wear a size 4 in jeans, but my stomach is so large my shirts don't fit right, and dresses? Forget about it. I've gone to plastic surgeons who tell me I need a tummy tuck, but not only am I too young, it will put me back 6+ thousand dollars. I'm at a loss....ad I have no clue what to do, any imput is welcome. Thanks!!!