off day with baby

My son is 6 weeks 2 days. He's normally very mild only crying if he needs something. But today he was just so fussy. His eating and number of diapers was normal, but it was just off. He wouldn't sleep like normal he would just wake up fussing. Tonight I gave him a bath and massage. I tried to feed him after and he ate maybe an ounce before he just fell asleep and didn't want to wake back up. I was able to swaddle him and lay him down with him staying asleep which never happens. I am sure it is normal for babies to have off days but this has made me so stressed. I keep checking to make sure he's breathing. Does anyone have any words to put my mind at ease? This is my first baby so I'm sure this is just my inexperience.