Hellow, oral thrush alone is not a reliable indicator of HIV infection, especially since you have taken multiple fourth-generation HIV tests, all of which came back negative. These tests are highly accurate after the window period (4 weeks post-exposure), meaning your negative results confirm that you do not have HIV from this encounter.
Oral thrush can be caused by various factors, including stress, antibiotic use, immune system fluctuations, dry mouth, or other underlying conditions such as diabetes or nutritional deficiencies. Since it has persisted for months, it would be best to consult a doctor or dentist to investigate possible causes and get proper treatment.
Independently of this episode, for people with occasional partners, it is always beneficial to undergo routine screening for sexually transmitted infections.
Best regards,
Prof. Giovanni Guaraldi