Glad Paul and Scott jumped in, they are daily wrenchers with a fokton of experience...
So how much oil did you drain out?
Also strain the oil that came out of it, and look for debris that might have been gathered on the pump screen. See if you got any metal in there, even glittery look to the oil.
If you can, cut the filter apart to see what you have in the pleats?
Now that you have oil pressure, peek into your rocker arms now, and you should notice a big difference in oil coming out of the rocker tips...it should be squirting, not just a dribble out of the rocker arm hole (pushrod tip)