Have a lunp under my armpit its not near my breast but like in the mid/lower part i did shave the other day and used new deodorant. what is causing it?

Watch for infection: There are lymph nodes under your armpit that can swell and become tender if you have an infection. You can also get an infected hair follicle after shaving that can cause a lump. If it's red and tender, you can try using warm, wet compresses and watch for worsening infection. Get an exam if infection worse. If not tender, monitor until after your next period and get an exam if it is still there