How To Treat Circular Mark On The Inside Of Left Thigh?

Hi. I had noticed just before Xmas that I have a circular hickey like mark on the inside of my left thigh, probably about 20cm diameter and not very dark. Though more recently I have noticed that smaller, darker, rash like marks, about half the size of your small fingernail have appeared in the surrounding area that are moving lower and around to the back of my thigh. I thought that this may be related to a travel related sickness I experienced while in Vanuatu in November. It's not shaped or in any way looking like ring worm and I know it's hard to diagnose without seeing the problem though at this point any opinion is welcomed.