Why wont my boyfriend answer me?

on sunday night the 26th, he said he wasn't feeling good and his temperature was 104.5. he was still using smiley faces when he was texting that night. i decided to let him rest and told him to text me when he felt better... he said "i'll text you tomorrow... i'll feel better by then :)" it's now the 28th but i'm worried that he just might have made the excuse of being sick so he didn't have to talk to me... any ideas of what he might be doing and why he isn't texting me?