Help with weird discoloration

Hi, I’ve had some trouble with these weird dark spots in my armpits. Ive went to the doctor and they told me to put Vaseline but it wasn’t really helpful. Sorry I tried to markup my unshaven armpits lol. If anyone’s had this let me know what you did to get rid of it! It’s really taken a toll on my self confidence as I feel I can’t wear certain shirts without feeling self conscious.