It does sound like you may have IBS, but to rule that the case you'd have to get a bunch of test done to rule out anything more serious. Stress has a really weird way of interacting with your insides!
For the next two weeks try taking Metamucil 3 times a day coupled with Pro-Biotics at the same time. You can pick up pro-biotics at your local drug store, I take something called acidopholous and it comes in pill form... it should be with the rest of the vitamins. It replenishes good flora in your gut to help ease diareah and constipation. It will also ease up your gas and bloating. Call up your doctor to make sure taking the pills is OK, just to be safe it doesn't interact with your medication.
Start eating a lot of fiber (Bran, raw vegetables, fruits...etc) and drinking LOTS of water when you do to bulk up your stools.
You have to make sure you eat! Limit processed foods as much as you can, try to limit your intake of red meat as well. Not saying to completely cut it out, but tone it down if that's all your snacking on all day past breakfast.
If you walk alot, that should be enough in the way of helping your bowels. A good walk after you eat can help move things along.
After a 2-3 week period on this regime, if you're still not feeling better - check in with your doctor to see if he/she wants to run any tests to make sure it's not something more serious.
Hope this helps