no oil pressure.. help please

[RedHeartbeat]

hurting the oring on the oil pickup tube will cause this issue.

[farmtruc]

There's no reason why the oring would be damaged just by changing the cam, unless you removed the pump or pickup tube for some reason.
You possibly damaged a cam bearing, or when the cam was installed, the cam bearing decided to spin or come out.
I've had this happen before: changed out the cam, get everything together with no issues and NO oil pressure! No reason to it. Ended up being the oil pump.
I'd change the oil pump first, then if you don't have pressure, the cam bearing is screwed.
I just pulled an engine last week that had a bad cam bearing, you'll have to pull the engine and take it to the machine shop for new ones.