The fact that you are posting here , you have an idea what paranoia is. Now whether your suspicion is justified is anyones guess. Practically speaking , are you seeking professional help for any mental health problem? You also seem to be in the area of not having the ability to check and clarify if this guy is indeed suspicious. People who suffer delusions and paranoia begin to make assumptions because they can not clarify a situation in a practical and communicative way. Im not saying you should walk up to the person and start accusing him of anything. But you do say that something is always blocking you from getting a possitive profile of this person. He is either on the phone or his moustache is in the way. So I would say , does he have or does he not have a moustache. If the answer is sometimes , it becomes less believable.

Also why would someone be fallowing you , are you attractive? Is their any reason you can think of.

Bear in mind that truely paranoid people have especially odd reasons why they think they are being followed.

Regardless , I would talk to your gp or local docter and just get a sounding on it. Also have you spoken to a parent or trusted person about this. Communication is important.