Is it normal to be tagged as straight even if i'm a lesbian

I am a lesbian but I have a very difficult time trying to hook up with girls, since everybody thinks I am straight right away.

I end up telling every girl I like that I am a lesbian, but it is not very exciting to be that literal all the time.

I also think that my gaydar needs to be tuned, as most of the girls I end up interested in, are just straight... Is t normal?