Tips on being alone with the baby at nights?

I had my baby august 25th at 35 weeks. He eats about 2-3 oz every 3-4 hours. I've been noticing recently that he wakes up about an hour or so after I put him down for bed and then is awake for about 3 or 4 hours fussing. The doctor told me to let him cry for a little because his tear ducts aren't fully developed since he was born early and the crying would help his eyes clear out. Well anyways, after I feed him change his diaper and burp him and all he would usually fall right back asleep until the next feeding, now he just stays wide awake for a few hours after. Any tips on helping me at nights? My fiancé just went back to work this week and he works nights.😔