Seroma can be a trial. Some of us leak for longer than others. It's very important to keep track of what is going on--keep notes of the amount of fluid that was withdrawn and when. All this stuff is on your record, of course, but having those figures at your fingertips is helpful if this blows out into a situation that needs fixing. The underarm boob thing is creepy--i had one that persisted for weeks. Because of the nerve damage from the surgery it wasn't painful and I had it drained about twelve times before it finally buggered off. What a nuisance. Hope yours resolves quickly.
I don't know a bra will help, I tried a racer back sports bra thinking the compression would help, then I couldn't get the bloody thing off. I felt like I was being eaten by a boa constrictor. I coudnt make my arm bend the right way to pull it over my head and the pressure was unbearable. Being a racer back I couldn't roll it down and step out of it. In the end I made it to the kitchen with one arm stuck over my head and a Lycra tourniquet wrapped around my body and took to it with the chicken scissors. Brings a sweat to my brow even now, just thinking about it.