Why do girls look at some women and laugh? or give dirty looks?

I'm just wondering because I feel REALLY insecure. I don't like it when people constantly look at me or give me dirty looks because I honestly am not happy with how I look. I am constantly told I'm nuts and stupid and I am good looking and really pretty but my brain makes me think otherwise and I'm paranoid. but I don't know. I'll be out with my boyfriend at a really public place with people of all ages and I will be standing with him and I'll notice a group of females giving me dirty looks and looking me up and down, when I notice them they'll group together and talk then look again at me. I've noticed this happening to other women to not only me. I'm just very observant. I don't dress overly revealing or anything bad...i just like to dress sexy/cute...or try at least. this usually only happens with females my age or younger but sometimes women a little older do it too. but it usually stops with women in their late 30's+ since they are mature and are pretty much over stupid stuff... Show More