I was also diagnosed with IBS when I was very young (I'm 54 now.) It's not really a true "disease" but rather a default diagnosis. That means that after doctors rule everything else out, they lable you as IBS.
In the last few years, doctors have added a letter after it; either IBS-D (which means you have diarrhea) or IBS-C (you're constipated all the time.
Like you, I've got IBS-D. In my opinion, you should be tested for everything you can to make sure nothing else is going on, before accepting the "IBS" label (I've heard one doctor say the other physicians joke about IBS saying it stands for "I'm Basically Stumped.")
If you DO have IBS, you're going to have to do a lot of trial and error to see what works for you. There are a lot of drugs available now to help treat symptoms, but many have side effects. That doesn't mean you shouldn't try them, though.
Through my own experience, I found that the two biggest things that helped my IBS were:
1. Exercise. I began jogging daily in my late 20's. 30 years later, my joints and back can't take the pounding of running, so I've switched to walking, and a stationary bike. Regular, daily aerobic workouts definitely helped my stomach.
2. Keep a food diary: Write down every single thing you eat every day and then, how you feel an hour or two after. You may begin to notice that certain foods don't agree with you. I love to cook, but I can't tolerate anything hot or spicy. I cheated last week and had buffalo wings at a restaurant with my best friend. Oh. My. God. That night AND the next day, I had horrible stomach pain and diarrhea. I can't eat citrus fruits either, which is a total bummer, since I love grapefruit and oranges...but they're on my NO-NO list now.
3. Don't eat large portions. This is huge for me. Eating a full meal always ends up with me getting sick. If I have sandwich, I'll eat half. If I'm hungry an hour later, I"ll eat the other half.
4. Watch out for protein. It's super healthy for you, but protein molecules are very big and take a long time to digest. I can't digest protein shakes or bars; they make me sick.
Cut out all soda; especially diet soda. You mentioned Lean Cuisines. The good part about them is that the portions are very small, but the bad part is that they are heavily processed...lots of preservatives, etc.
I try to eat as cleanly as possible...meaning no processed foods or anything with a lot of ingredients. I have melon for breakfast...a salad for lunch, and dinner is just plain chicken (grilled or baked) and brown rice.
I stay away from cruciferous vegetables like cabbage, broccoli and cauliflower. They make me gassy, bloated and nauseous.
Good luck to you, sweetie. IBS is an up-and-down thing. You can go for months and feel good, then have flare up and feel miserable for weeks or longer. As I mentioned, you have to be your own detective and figure out what your body can tolerate and what it can't.
Let me know how you're doing..and good luck. -Home Chef