Lump in armpit

Hello. I found a lump in my right armpit about 2mths ago. I check regular due to family breast cancer. Anyway the lump goes very big and hard then after a few days fluctuates. The gp felt it and has organised a scan. Im going next week. I also have sjogrens disease which im told can make me more at risk of lymphoma! Any ideas what it could be. It doesnt hurt. Thank you