Is it normal that i can't stop thinking about being with a girl?

I am a female in my mid-twenties. I've always known I was bisexual, but I've never had any experience with women. My first relationship lasted 3 years and I was perfectly satisfied with my boyfriend. After that, I dated a few different guys but wasn't finding myself satisfied. Then I had another long-term relationship with a guy and it was going well up until about 9 months ago when I started to have stronger feelings for women and started really desiring to be with one (sexually). I felt extremely guilty because I was fantasizing about girls and sometimes even during sex I would pretend I was doing those things with a girl instead. It broke my heart because I loved him, but I had to end the relationship and we've been broken up a month. Now I find myself fantasizing about being with a women constantly, all day. It's very distracting and frustrating! I sit in class and imagine what it would be like to have oral sex with certain girls in my class. I literally cannot get these thoughts out of my mind and sometimes I feel like I'll go crazy if I can't go down on a pretty girl soon. I find myself attracted to more girls whereas it used to only be the odd one I felt feelings for. It's driving me nuts! I know it will be a long time before I can find the right person to have a relationship/experience with because I'm shy, very feminine and no one would know I was a lesbian or into that. I feel like I don't know how long I can wait though. I really don't want to do something like find someone random online just to have an experience with because I'm not that kind of person and I would like it to be with someone I actually care for and for it to have meaning. But I also feel like I'm going nuts and it can't be healthy to be this obsessive and have my mind preoccupied with sex 24/7 because I can't fulfill any of my urges. Do I need help??