Trichomoniasis - If I took the first 2 doses of Medtrozidazole && had sex with someone I didnt know?

If your random was infected, you have it again. If he did not have it you have given it to him and the decent thing to do would be to phone him and tell him to see his doctor for treatment or prophylaxis to prevent the parasites becoming established.

It's a shame that you have such a cavalier attitude to spreading an STI (I'd expect it from a man but not a girl). I wish the stranger all the best and hope he gets to learn a lesson also. Sadly he will be also be spreading the love for quite some time, unless you can get in touch, as it is almost asymptomatic in men.