The symptoms that you have described suggest that you might be having "pityriasis versicolor".It is a fungal infection
which can present as hyperpigmentation
of the skin due to destruction of melanin in the melanocytes (cells which give colour to skin).These hypopigmented spots dont get tanned.I suggest you take bath regularly and wear clean,washed clothes daily.I also suggest you consult your dermatologist
who will examine you completely and prescribe you Fluconazole tablets and selenium sulfide
shampoo to apply over the skin for 10min before taking bath.It will usually take some time for the normal colour to come back in those spots.
I hope it helps.