
This seems like a very serious diagnosis with very little investigation, has a nasty urine infection been ruled out by obtaining a sample for testing initially for protein which indicates infection and then lab test to get what bug is responsible and correct antibiotics given. How has the pup managed his weeing for 6 weeks or is this a problem that can develop some weeks after birth?
I know from person experience how painful a UTI can be when a locum out of hours GP gave the wrong antibiotic even when I said I'd not known that to be used for UTI's, he didn't change his mind,by the Monday morning my wee was like pea soup and brought tears to my eyes each time I went to the loo despite drinking 4 litres of water to dilute the urine so it wouldn't hurt so much, it took 2 courses of antibiotics to clear the infection and 2 weeks for the pain to stop.
If you have not had the urine tested then put a clean bowl between your knees and hold the pup over the bowl whilst giving him a drink it may take a while depending on when last wee'd, we used to do this with little girls on the prem unit, little boys were easier because we had tubing which fitted over their winkie and we just kept checking for a result periodically.
I truly hope it isn't something so serious as to mean he has to be PTS.