My baby has been fussy lately too! And he never was before. I think he’s definitely going through something. He stops fussing if I hold him or give him a teething toy lately.
Mine is 5 months and 3 weeks also. I literally googled “why is my baby grunting?” yesterday 😂 Read some different articles that pointed to it being a developmental stage! Part of finding their voice. Mine is grunting when she’s being silly and fussy - so hard to tell if it’s caused by anything else!
Maybe teething? My pediatrician said at this age their gums are “hardening”