Random small light brown mark on hip that fades and returns….?

ive had this mark for over 2 years now. It all started when i was sat on the beach with one of my mates. she turned to me and said ‘oo is that a birth mark?’ confused as i have never had a birth mark (or an obvious one) i had a look and noticed that i had (and still have) a very small, ‘bone shaped’ light brown mark on my left hip.

I put moisterising cream on my legs, and i had never noticed it before, so i know that when she said it, it couldnt have been a birth mark as it had randomly appeared.

I dont no whether it could be anything to do with the sun? It seems to fade to almost unoiticeable – and then suddenly returns back. I noticed that it seems to return more when im in swimming pools oddly enough?

Has any one expereinced the same thing? or something similar?

Im not worried – just curious as to what it could be?