What is causing the rash on my armpit?

[Erocs]

Can I include a picture somehow? It's dark red, it burns/stings, it leaks some pus but doesn't look like a zit and is the size of two dimes. It hasn't grown. I've had it for almost a week. I have used a new deodorant for the last 2-3 months that has caused my armpits to itch slightly but never a rash of any kind. Just dried them out I think and I kept on using it because I am cheap and my wife had just bought a few on sale. We went on vacation and I had an old kind of deodorant that I switched back to and that's about the time I noticed the rash. It didn't really hurt at first until I put hydrocortisone cream on it for one day and then it really started hurting. I could be wrong but I don't really think it is deodorant related or else I would have a similar rash on more parts of my armpit. It's just in one place near the edge. I am not sure the cream is what fired it up or if it just coincided with an increase in intensity. I haven't used any deodorant or any other creams for 2-3 days now and it hasn't shown any signs of progression.