We are all different when it comes to sex. Some people may find oral sex amazing and you may prefer something else.
From your post I'm assuming you are quite young, and the girls performing the act are also young? This could be something partially linked to experience - like everything technique is important. You don't say if any of these are long term girlfriends but working on what you enjoy and learning about your sexuality is important - communication and remembering to return the favour.
Make sure you're clean (shower) and have somewhere safe where you won't be disturbed. Being conscious of other things makes it harder for you to relax and get into it.