IBS and Giardia

We're not doctors here so we really cannot give medical advice. That having been said, how long have you been taking antibiotics? They can take a few weeks to run their complete course. In the meantime, you have to keep taking them, you can't just stop, even if you feel better. This is because the bugs the antibiotics are supposed to be killing can still lurk for a little while longer, even if you don't feel any symptoms.

Chances are that your doctor tested you for giardia. It's a parasite so you either have it or you don't. I highly doubt you'd be told you have it if you were not tested for it, or if the test was negative.

If you are unhappy with your present doctor, see another one and get a second opinion.

doctor didnt test me she just assumed i had it form my symtoms

Agreeing in advance with jespah, that is odd. I know of no symptoms or syndrom exclusive to giardia. It's a little flip to suggest a change of doctors over one issue, but are you really comfortable with this one?