Three months is generally the longest period to wait for greatest accuracy.
That said, the risk of transmission in someone with KNOWN HIV in this instance is between 8-11 in 10,000. This figure reaches zero if the individual is on treatment with good response.
In addition, oral thrush isn't associated with HIV as such. Oeseophageal thrush is associated with AIDs (i.e. advanced HIV). You wouldn't have gone from contraction to AIDs within a month, and you only have oral thrush.
tl;dr - Chill out and be more careful in future.