You shouldn't need more than a small bowl if you've only smoked 8 times. I was still doing wOnEeZ at that point and getting damn high. The only thing I can think of is that there's a flaw in how you're smoking it. Even week grass should do the trick for your ninth time, especially if the first 8 weren't all in the last month or something.

If you're not doing this already, try allowing your nasal passage to remain open while you toke. Suck the smoke in by drawing your tongue back into your throat, like you're sucking from a straw. Then hold the smoke for a second where the back of your mouth meets the back of your nose (like you're smoking a cigar), THEN suck it down. Hold it down for a good 5-10 seconds.

(I know the cannabis home fact says that you can exhale immediately, but in my experience, if I don't get a lot of air mixed with the smoke I have to hold it down long in order to get the most out of it - depends on how well your pipe hits.)