Stressed out.

I love my son to death but being a SAHM is wearing me down! My son is 4 months old and I feel like every day is the same, days run together and weekends don't even matter. My fiancé works really long hours and sometimes is home when the baby is already in bed for the night :( 
Yesterday my son wouldn't stop crying and I lost my temper and yelled at him and instantly felt awful! I spent all day crying and telling him I was sorry mommy is just really stressed. I've been cuddling him all day today. 
I'm lucky if I shower every other day and my hair is always a complete mess and I wear my pj's all day cause we don't go anywhere. I feel gross and run down. It's just hard sometimes. Anyone ever feel like this?