The question is, how do you know it's the same guy if you can't identify the way he looks? Can this be coincidence? Try to think this through. Is it possible you are making yourself hyper-aware in thinking someone is watching/following you, and so you are noticing men you happen to be looking in your direction and attribute it to being the same guy?

This can be a rocky road. If you are having low-grade paranoia or delusions you can actually talk yourself into them more if you're not careful. It seems you have some insight that maybe what's happening isn't realistic or logical or you wouldn't have posted here, and that's a good thing.

As the previous post said, what is the reason you think this person is following you? That's a key element.