Please help me understand if a specific persons tracks me on-line.

There is a girl that likes me and is very persistent. She doesn't have my email or my phone number. We are friends on a Russian social network I have noticed on a few occasions that she posts same songs or otherwise reflects on media that I consume. Some of it could be explained by very close attention to my profile (like when I add a track to a bunch of hundreds of others), but some can not. Most recently she posted two songs I listened to on Youtube. I do not have an account, I didn't comment on these songs, I didn't like them etc - there was no way anyone could have found out. And these are little-known Italian songs of the 60-ies, can't be a coincidence.
I checked my PC with Dr. Web and Advanced System Care, which found no security flaws.
With that in mind, where should I start in order to understand if I am being spied on?
Thank you in advance.