My DS sometimes squirms and grunts a lot when feeding, especially when he's been latched on for a while. He also likes to be upright when awake and I've read that these could be symptoms of reflux. Is this something he will grow out of? Is there anything I can do?(He is 5 weeks old)

if they're the only "symptoms" then i'd say no.
a lot of babies squirm and grunt when feeding, because it triggers the poo-ing reflex which can feel weird/uncomfy to them. and they're quite noisy feeders a lot of the time anyway tbh
mine have both liked being upright all the time, and neither had reflux,
hth

Its possible, but they aren't the only symptoms. They may just be his personal preferences!

Does he appear distressed during or after feeding? Vomiting at all? Putting on weight OK?

If he's quite happy in himself otherwise, gaining weight nicely and feeding well, there's nothing that you need to do.

Thanks a lot, I'm probably being paranoid.He's putting on weight really well and does vomit but this is only occasional. He does get distressed during feeding and will cry whilst latched on (if this is possible)! I have to stop and hold him upright and then he quietens down. Sometimes it'll mean he won't be able to feed well as he keeps wriggling himself away from me.This has only been happening in the last week or so, before that he was fine.

That is exactly what my dd has started doing. She is same age and at times is very wriggly, looks quite uncomfortable and keeps pulling off, but then seems to want to go back on. I have to put her upright ovwe my shoulder to calm her down and then try again. I was wondering if she had colic, but she doesn't really cry that much after the feeding has stopped so I'm not sure if she does....