I've been smoking for 6 years now, and i often find i have the same problem......i can't get high or it just makes me so fucking sleepy that i'm not having fun. Here are a few hints.

Change Dealers: try finding a different strain..maybe the stuff you've been getting is crap, you've smoked that variety for too long, etc.

Use a Different Method: like everyone's said, get high a different way. I have a Volcano Vaporizer and I fucking love it its the best thing, but when i want to get seriously fucked up, i make brownies or smoke a blunt.

Take a Break and be ALONE: i've tried (and failed) several times, so here's my solution: portion control...smoke the herb like you're on a diet. Try smoking only 1 joint a day BY YOURSELF. I get a lot higher by myself than with my boyfriend or ppl i smoke with all the time. Don't make the doobie too big, and try to clip it half-way through. Smoke slowly....you'll realize you're stoned sooner. It's like eating...if you eat too fast, you get that horrible "i'm too fucking full" feeling. It takes 20 minutes for your brain to realize its full...takes your brain less time to realize its high, but it still takes time. Slow, alone, relax and enjoy.

Let me know how it goes! I hope I helped!