Can I be honest with you all?
I Suck at Sex Scenes, every time I try, my brain goes blank, especially since most of protagonsits are either Lesbians or Bi-sexual/
Any advice would be great!
The first bit of advice, if you're adamant about including them, or genuinely want to improve your writing of them, determine the overall tone of the scene as compared to the rest of the story. Are you writing a serious, intimate, moment between the characters, or just for the fan-service?
If it's the latter, I'd say to reconsider your approach, and whether or not the scene is actually relevant to the narrative itself. If it isn't relevant or necessary to the narrative, then there's no real reason to include it.
The second point I'd direct your attention towards is the characters in the scene itself.
Why are they having sex? What has their relationship been prior to that moment? What will it become after that moment? Who wants the sex, and why? How does the sex scene serve to enhance their characters and the dynamic between them?
All of that should definitely be sorted out before you even start thinking about writing the scene itself, because if you haven't addressed it, there is a good chance you'll end up not doing justice to the characters as you've written them prior, and the scene will come across as forced.
As for writing the scene itself there should always be a lot going on beneath the surface.
From what I've seen as well, too many stories here focus just on the actions, and they neglect the characters themselves. The build-up, push-pull dynamic, intimacy, desire, and all-too-important foreplay and after-care. Of course, I've also seen my fair share of exceptions to that as well.
There's no real magic formula though, beyond keeping the scene's focus on the characters in their entirety, and having it serve as the culmination of their romance arc (in most cases). Ultimately, everything in the scene needs to stay true to who the characters are.
If you are trying to elevate your scenes from 'smut' (porn w/ plot) to 'erotica' though, you need to shift the focus from the physical, to the intimacy and the emotional, narrative, and character developmental payoffs in the scene.
I don't have much advice beyond this yet, because I'm also still honing my craft in this area.