We just got back from a vacation in the Wi Dells. I noticed that I have a rash on both my sides by my breasts, going toward my back. Raised red bumps?
Swimmer's itch. Due to allergic reaction against microscopic larvae looking for their proper host, which is not you. Self-limited. Best relief from strong prescription steroid cream. Do not take Benadryl (diphenhydramine) unless you want sedation. It won't do much for you, anyway.
? Contact dermatitis. Is this where your swimsuit would be in contact with your body? If so, some allergic reaction with the swimsuit, water, etc. May use topical 1% Hydrocortisone and oral benadryl, (diphenhydramine) both these are available over the counter. However, if no better in 1-2 days, or worse, or other symptoms, please see your health care provider.