Is it normal that my 28 yr old husband isn't wanting sex?

My husband and I have only been together for 3 months, and we were having sex practically everyday and he was really into it. He even said that he had never gotten off with anyone the first time he was with them but he did with me. He got off with me almost every time. The only time he didn't get off was two different times when he had been drinking beer and hard liquor, but the very next day we had sex he got off. Then, all of a sudden, he started not getting off and i didn't think much of it until he hadn't gotten off three days in a row, the 4th night we didn't have sex, the 5th night he didn't get off, 6th and 7th night there was no sex, and that's where we are now. Things has never been this way. He says it's a mental thing and sometimes he isn't as sensitive and he is stressed and it makes him more stressed and embarrassed that he isn't getting off. He says his sex drive completely goes away at times. I have never known for a 28 year old to do this. So, is it normal or does he need to see a doctor or is it me? Sometimes I feel like it's because of me even though he swears it's not and he says he finds me very attractive and enjoys being with me.