Re: Is it IBS?
The burning in your stomach could be a GERD related thing. I have similar symptoms, which turned out to be small ulcers at the base of my esophogus at the entrance to my stomach. When I lie down, have an empty stomach, or a few hours after eating a large meal, I get that burning sensation.
The blood when you wipe is probably hemorrhoids. If you have frequent diarrhea or straining during movements, they're likely to happen.
Your legs may hurt after a BM because you are straining or just overall too tense. I can imagine it being hard to relax having a BM like the ones your described, but that tension isn't good for your muscles, skeletal or stomach.
As for the dizziness, do you eat regulary? Get enough iron? Any menstral irregularities? The dizziness may be from a loss of iron from menstral blood, or blood loss in the GI tract. Hemorroid bleeding wouldn't be severe enough to cause an iron deficiency, but if your stools are black or very bloody (not just a streak coating the stool) then you may be bleeding somewhere within your GI-tract. If your stomach burning is caused by ulcers, it could be possible that they are bleeding, but usually the pain is much more severe for a bleeding ulcer and you would have a lot of nausea/vomitting as well.
My advice would be to see a GI specialist, and maybe get scoped if you and your doc are concerned about ulcers. Hemorrhoids can be prevented with a high fiber diet, less straining and/or holding back the urge "to go." I've also heard soaking in the tub can help hemorrhoids as can keeping the external anus clean and dry as much as possible. For the stomach burning, don't lie down after eating meals (wait a few hours), and try to avoid taking antacids. Stomach burning can be a sign of not enough acid too. I find that saltines sometimes help ease the burning sensation.
I hope this was helpful, but my best advice would be to see a doc about it.