Anxiety. Any advice appreciated.

So I've never had a serious relationship but my current boyfriend of 4 months has dated this girl for about 20 months, about a year before we started dating. I have no concern that he still has feelings for her. I know he's over her. But still, I have such anxiety over his ex. First of all, she's a lot more popular and pretty than I am. She's super sweet and personable, while I'm kind of awkward and shy. I feel like my boyfriend is embarrassed of me. When we started dating, the only person he told was his best friend. I had to tell his other friends. I know he loves me, I know he only wants me, but why is he so reserved about it? I know this sounds stupid but he hasn't posted anything about me on instagram or Facebook. I remember with his old girlfriend, she got #wcw like every other week. It just stresses me out especially since people who are mutually friends with his ex are saying that she still likes him. I'm just so self conscious and I hate being compared to her, because I'm considered to be a "step down"