...Is it possible you have bugs? Are you indoors? In a basement, maybe?
Idk, man... It looks weird. It's not a burn, and I've never seen a deficiency that does that...
ph off?
It doesn't look that serious, right now. If it starts spreading, or getting worse in any way. Just start correcting possible problems. Process of elimination. Start eliminating possibilities.
Jonus is right. More pics and info on your room...