Help! how to settle 5 week old?

My son is 5 weeks old and feed. He's very healthy and has been gaining weight, 300grams per week but that has now settled down to 200grams. Some days and nights though he can not be settled. He whinges for hours on end and will only sleep for 10-30 minutes at a time and then try to feed, usually for only 10 minutes. I've tried other ways of settling him but what works one day doesn't the next. He sucks his fist a lot during these periods and at first a pacifier settled him but he no longer likes it. Being in the pram, going for drives in the car and soothing music are not working. I'm at my wits end and am exhausted as he's worse at night. How can i get him to sleep for longer periods and not want to constanlty feed? He has several "proper feeds" throughout the day where he feeds for up to an hour and is content but sttill has hours of wanting to feed every 10 minutes.