I Am Experiencing A Rash Under Both Armpits And It

I am experiencing a rash under both armpits and it is very itching and uncomfortable. Started on one side then the other. The rash is red and raised. Probably from the itching. I've used cortisone, baby powder, a healing cream (don't know name), and Neosporin which I have now been told that wasn't a good idea. Is actually worse today after putting the Neosporin on last night. I laid in the sun a few weeks ago and used a sunscreen, which Is the only thing I can think of that may have caused this. I use the same deodorant for years. I did get a few cortisone shots in my back about 3 weeks ago, so not quite sure if that could be it. They have a steroid in them, and also wasn't sure if it could be hormonal. Didn't have my period for months, and just started back 2 weeks ago. I'm obviously going through Peri-menopause.
Thank you!
Laura