Bowel Problems....Please help!?

I'm having trouble with bowel movements. It's like I feel like I have to go but I can't. I tried laxatives, I ate nothing what Raisin Bran for like two days straight, I've been drinking only water, etc. I've had more gas than usual, abdominal distention, major bloating (my stomach ballons to where I look pregnant.....and I've ALWAYS had a really tiny and flat stomach), weight gain (I've never gone past 124 and I'm around 130....and I haven't changed my diet). When I try to go, I get nothing, and it starts to hurt to try and force it. Or sometimes I get little pebbles. My stomach growls a lot. When I tried the laxatives (I tried 2-3 days).....I'd get REALLY intense abdominal pain. I don't know if it's from the laxatives or just in general because I've had it without the laxatives too. I'm really concerned. What could it be? What do I do?