Not sleeping

My almost 8 month old had been sleeping through the night since he was 2.5 months old. Now he is waking several times a night and is so hard to get baxk to sleep! This momma is exhausted and feeling bad for getting aggravated through the night. I started working full time 3 months ago. I am not sure what to do to help him sleep through the night again. In desperate need of advice!