Disclaimer: this is all from my point of view and fully accept that people may disagree.
I'm bisexual, and for me, attraction has at least two parts: sexual desire and a crush. Sometimes you get the sexual desire without the crush (like on a one night stand) and sometimes, although more rarely, elements of the crush without the sexual desire (like when you make a new friend that you get obsessed with - although rarely as strong as with a relationship post-teenage years).
For me, sexual desire, when it's strong, is like heat that spreads through my body. I can feel myself clenching 'down there'. I feel acutely aware of my skin; I feel warm; my inhibitions lower. I want to touch and be touched. It's a raw, needy feeling. It's physical as much as mental, although god knows, fantasies can lead to it and it leads to fantasies.
Incidentally, I have always felt that a classification needs to be added for heteroflexible/bicurious women, who would sleep with other women and find them 'pretty and sensual and soft' without ever really feeling any of the above.
A crush, I think, has already been explained as well as I can here. Butterflies, excitement, you would always want a text to be from them before anyone else.
Hope my tuppence helps. And I hope you figure it out soon. There are lots of LGBT friendly therapists in London if you're based near there (a lot listed on pinktherapy). It might be an avenue to consider if you wanted a more in depth chat about your feelings
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