Hi all you swimmers out there

I've been swimming a lot more this winter than before, and my swimsuit while still snug is getting a little sloppy and needs replacing. I also recently noticed I had these strange marks below my armpits/above my ribs on both sides, small skin irritations. Today one suddenly turned into a full skin burn an inch wide and 3 inches long (OW! ) and I realized it was my swimsuit causing them. Is this maybe typical for a swimsuit getting sloppy? I'm getting a new one anyway, but I was wondering if I should be looking for one with a different cut or if I'll be fine once I get a new one.