How long does it take for oral thrush to clear on its own?

Depends: I assume you are not willing to receive treatment and you are hoping that the thrush will clear on its own. If this is the case, then the thrush may never clear or may be present for a very long time. Get treated asap and find out the cause of the thrush. The thrush can resolve in a week with medications.

Requires treatment: Without a clinical examination it is difficult nto tell what your problem is but typically if you do have oral candidiasis (thrush) it typically presents a red or white patches in the on the cheeks, tongue, and back of the throat. This infection will not resolve on its own and requires medication (either topical or systemic). Please see your physician.