How do I convince my boyfriend that I'm not lying when I say I haven't had plastic surgery?

I started dating my boyfriend when I was 16 and he was 17, so naturally I was kinda underweight and had some issues with my looks, which healed as I got older. My body has started to grow, I don't look underweight anymore and overall I just look a lot better than I used to (I'm 19 now by the way). My boyfriend constantly brags about it and says that it's the "boyfriend effect" that has caused all this, but at the same time he constantly asks me if I've had lip fillers, buccal fat removal, rib removal, breast and butt implants and a nose job for some reason. I've repeatedly said that I haven't had anything done, and the fact that I have super strict parents who'll absolutely not allow it when I'm a teenager should put his suspicions to rest. He freaked out one day when he saw a stretch mark on my butt and thought it was an incision mark and bugged me about it the whole day. I've repeatedly told him I've not had any plastic surgery but he doesn't entirely believe me. At first I liked it and considered it a compliment, but now the constant nagging has become annoying. What do I do to get him to stop?

How do I convince my boyfriend that I'm not lying when I say I haven't had plastic surgery?
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