Forearm Lump: Causes, Symptoms & When to See a Doctor

Question

The lump   I got a zit looking bump on my left forearm about 2-3 weeks ago. It was small and itched a bit. I dismissed it as a zit or spider bite and forgot about it. Just lately, the last week or so, it has grown in size (dime size?) And has become very, very sore. I can't put pressure on it or brush up against anything. I saw what I thought was a white head on it a week ago and attempted to pop it with a tack. Nothing much came out just a little puss and blood. Since then it has not gotten any better, but I dont think its worse either. I can feel hardness under the skin in and around the lump. Also there is redness surrounding it. It doesnt seem to itch anymore, and i see no bite marks from a possible spider. As i said it is very sore, tender, and feels a little warm. I had the methotrexate shot 3 weeks ago for an ectopic, and I know that can lower immune systems so I am a little concerned. Can you please tell me what it could possibly be? Should I see a doctor? Is there anything I can do for it at home? Thank you so much!

Answer
I would check with your doc, the picture doesn't help me (too blurry) but I suspect you have a low grade staph infection on your arm..... if not allergic, I would use some septra antibiotics and consider a little drainage (past sticking a thumbtack into it)     

These are prety common.....