Eczema or skin fungus?

I have eczema and i get these white spots on my arms but its only in the summer. I also read white spots could be caused by a skin fungus. So now i dont know which one it is and whatever 'it' is, i really want it to go away because it makes me so self conscious of my arms..more than i already am because of other eczema spots. And i dont get why it just appears in the summer also...help?