Advice, please

Hey everyone! I've been visiting these forums for a while, but this is my first time posting anything, so go easy on me, please!

I just recently tried air inflation for the first real time. What I mean by that is, I've tried it just to see what it felt like before, but this time I was going for the full effect. Anyway, so here's my method:

I washed myself out with the shower hose, making sure to get all the water back out. Then, I laid down on my bed with my aquarium pump, put the hose in my anus, and turned it on. It was going smoothly for about two minutes, but at that point I began to feel a little uncomfortable. I read a little discomfort was to be expected, so I kept going. At about three minutes, I was feeling quite unsettled and started cramping, so I stopped.

Now I expected to cramp up eventually, but not so soon. What was really disappointing was that I didn't get very big at all. Like, virtually no difference. I DID feel very bloated and gassy, and it took some time for it to work itself out.

Basically, what I want to know is what (if anything) did I do wrong? and how do I actually get bigger? Is there anything more you need to know that might help your answer? I'd really like to get as big and round as some of the girls on Youtube, and maybe post a vid someday.