Cyst on thyroid

Has anybody else had one? I got out of the shower like 4 weeks postpartum and looked in the mirror and noticed a lump but didn’t pay it any attention. Went to my 6 week checkup and sure enough she said

I had a lump on my thyroid. Went for ultrasound and it’s bigger than a grape but smaller than a golf ball. Said my levels were normal and they will check on it every year. But I’ve been gaining weight and I’m not sure what to think of it. How often do they test your levels? I know cysts can pop so I’m scared of that. Anybody have any advice? Thank u