I also have Giardia, CFS, Toxoplasmosis, Lyme, Candida overgrowth and parasites. And I think that most bacterial and viral problems result in having a parasite infection.
My worst symptom is dizziness, sometimes with intense feeling of faint or getting a stroke.
I would recommend to start with parasite cleanse. There are some very good products, like Humaworm or Barefoot DeWormer. I would also recommend liver flushing. Enemas can also be very helpful.
Please check Dr. Sutter's board in CureZone.
Maybe MSM could help you fighting Giardia. Have a look in Google with "Giardia" and "MSM", you'll find some information there.
I have massive bloating in the upper abdomen, but it depends not every time on eating. It often comes without eating anything. My main problem is "my" tapeworm. It is, what makes the bloating, the aches, the dizziness.
Ornithine is helping me with the dizziness, also enemas. And I've started with liver flushing in 2006 and have made 21 LF up to now.
I've made a big mistake with deworming. Since I know about the parasites in me (it was in autumn 2006 when I saw the tapeworm progottides the first time) I started with deworming (several things, Humaworm, Clarkia and so on) BUT not continiously. That was a big, big mistake.
Now I'm deworming constantly, make liver flushs every 1-2 weeks, enemas, zapping and plate zapping.
And it's getting better. But round the full moon or new moon it's getting worse :-( That last a few days, then it's getting better.
Don't give up, start constantly deworming, read on Doc Sutters site, and I hope, you will get better very soon!