Any news back from the GP yet?
I'm sure that he'll get you in on Monday - they always have spaces for emergencies, or they'll cancel patients coming in for routine non-urgent treatment.
If you don't have any joy though, I would definitely take him to A&E. If you say he's had a bump or something, and you just wanted him checked over, and just mention your ongoing issues, then they will probably just do the scan there and then if possible, or admit him until they can do it. They might know what's really going on, but I'm sure anybody with kids would empathise with your situation.
(((((big hugs)))))) Hope it all gets sorted soon.