5 weeks ago I have received an unprotected blowjob from a prostitute and ever since I have been worried and a bit paranoid that I have sti or std. It only lasted for like 5 to 8 minutes and I did not ejaculate inside and she was using a mixture of her hand and mouth. I have asked her a day later if she has any sti or stds and she said that she doesn't however people can have it without them knowing, which is why I am concerned. We did not kiss nor did I touch or lick her vagina. Should i be concerned or worried and what are the chances that I have an sti/std?