Went from 165 lb to 145

(20f) this happen to anyone else so drastically? I used to eat a lot, like a lot a lot. Now I've been described to eat "like a bird" and whatnot, mostly just having a couple of chips, some apple sauce. The most I've eaten recently was some delicious tonkatsu and takoyaki. Very large dinner, but still not the usual for me anymore. I started taking lamotrigine last year in June, started off at 25mg, now I'm at 100mg. I am not very active. Is this something I should be concerned about, or is it fine and this isn't the biggest weight drop? I still drink plenty of water, by the way. When I first started, I starved for days because my appetite was gone. Now it's just small.