You cannot spot reduce. Unfortunately for you, this is where you happen to store your weight. For me, I would LOVE to gain some in my heinie, but that happens to be the LAST place I can. Always tummy first. pfft. lol.
So, you are going to need to lose all the weight to lose the man boobs.
And sweating doesn't lose fat, it just sweats out your electrolytes and sodium, etc, past a certain normal level. Make sure you stay well hydrated if you are sweating that much!
Or, you can always take the easy way out, and go for surgery, but then you'll have some nasty scars!