18 year old girl , diagnosed with hyperthyroidism

I'm an 18 year old girl and have been diagnosed with hyperthyroidism for a year; currently taking Carbimazole for it. A week ago i found a painful lump under my left underarm. About 3-4 days later i found another painful lmup under my right underarm. The next day, the pain was gone from my left underarm but the lump is still there. It only hurts slightly when it's pressed. Today, i noticed that the lump under my right underarm is no longer painful, just slightly when pressed. But the lump is still there. My breasts have also begun to feel sore recently. The lumps feel somewhat tender and rubber-like.However, i did shave my underarms about 2 days before the lumps appeared.I checked the blade and found it to be rusty. Today i've developed a slight sore throat and skin rashes

I have no known cases of breast cancer in my family, though i've not been eating or sleeping well for the past one month, in addition to being under a lot of stress.

Please help me, what could it be? Thanks.