I just want to sleep all the time

My baby is 7 months old and is sleeping good again, but suddenly I'm exhausted all the time and the only thing I want to do is sleep. I take naps when my baby does and then when he wakes up we go in the living room and I sleep on the couch while he plays in the floor for about 15 minutes (i know shame on me for not watching him). I'm a single mom, but I haven't been this tired since he was a newborn. anyone else have this problem?