Well the fact you felt bad with the garlic does indicate yeast dieoff.
As for Candida becoming resistant to garlic this is highly unlikely and AFAIK resistance to garlic has not ever been observed in Candida probably due to the mechanism of action of highly unstable sulphur compounds.
IMO don't stop taking the garlic, not ever. Other than that I can only recommend that you see a qualified naturopathic doctor if you've had no constructive dialogue with your chemical allopathic doctor.