Random Lump

Has anyone ever had a lump in their armpit? I've had this lump in my armpit for about a week or two now and it keeps getting bigger. It's red and it hurts even when I stretch. It's not an ingrown hair as I hadn't shaved for a couple weeks. I shaved to get a better look at it. It has no pus at all. I'm kinda scared it could be cancerous. I had went to the doctor when it first showed up and they gave me antibiotics but it didn't go away it got bigger.