Not sure what's wrong

My baby boy is 7 months, lately hes been cranky which is not really like him and he hasn't been wetting enough diapers the past few days. He is eating more food now and doesnt drink a full 6 ounces every 4 hours like he usually does, drinks maybe 5. He was slightly hot a few nights ago, temp was 37.8. I'm thinking the heat could be a factor in why he was hot but he was fussy. The fact that he still wants to eat is a good sign but am I overreacting? Should I take him to see a doctor because hes not wetting enough diapers? He pees but not as much as he was before. I used to change him 4 times a day, lately I haven't had to as much because it feels dry. I dont really want to sit in emergency for hours if I'm overreacting but has any mom been through something like this with their baby?