I have been playing trumpet for about 2 1/2 to 3 years now and i practice alot but my lips get numb to quickly. I can hit the octives when my lips are fresh but after about 30 mins` I can barley hold G off the scale...I really need some help.....I use a 1 and 1/2 C...does that matter at all or is it just me?..What are the differences in mouth piece sizes anyway??????????

Lip strength is not the issue. Many young brass players apply more pressure as they play higher in the instrument`s range. Some of us older ones do the same, at times. The factor that enables you to play higher is air speed. Oddly, more pressure, at least to a point, can push your lips together and reduce the size of the opening. The result - more air speed and higher notes. The problem is two-fold. 1) It only works up to a point, where the extra pressure actually starts forcing your lips apart, which slows the air speed. 2) It cuts off the blood supply and your lips get tired.
My suggestion: read Claude Gordon`s book on "Trumpet Playing is no harder than heavy breathing" or something like that. Then practice what he says on Clarke studies.
Good luck.

there`s a pensil exercise. take a pen or pensil (unsharpened end in your mouth), in your mouth and try to hold it in a horizontal position for several minutes without biting it with your teeth. you should only use your lips. works like a charm.

Well you could try to get a bigger mouth peice. I try getting a 7c....5c maybe. Thats probably your problem.

lip slurs

My teacher said the same thing. Slurs and a pencil. Mucho flexibility studies.