Big worry

Hi, I'm worried I may have contracted hiv. I'm a man who met another man online, went round his and went down on him for a minute or so, there was a little pre ***. I didn't like it and left. What's worrying me is that I had an ulcer and burn in my mouth. What's the likelihood Iv caught hiv? He said he tested negative 6 months ago but he might be promiscuous. I can't get tested for a few weeks or something and I'm worried sick.