I took my bathtub out and built a shower and it will not drain. The I can push the water through the pipe with a shopvac and I put a drain snake in and it came out clean and definitely went far enough. The P trap is at a 90 Degree angle. Will this cause a problem?

I'm not exactly sure what you mean by the trap being at a 90 ? If you installed a trap directly under the shower and ran it over and down the tub drain then it's double trapped and will not drain. The trap should be directly under the shower drain, and run horizontal til it's vented before dropping down.

To add to North Carolina's post, ideally the drain should be 2" all the way to the horizontal line. Most tubs are 1 1/2" and not adequate for the volume of water dispensed by shower valves. Also be sure your strainer is clean and not contributing to the slow draining. Venting is important also, so be sure it is vented properly.

Thanks you answered my question, the setup is fairly simple the P trap is the type you can screw together and were they connect it is not strait.

My problem if I read this correctly is that I did not vent it.

More likely, from your description is that you "double trapped it". Not having a vent does not prevent draining, unless you also have some other problem. In fact, a lack of a vent usually causes the drain to work TOO GOOD.