@miserystoy first of all , happy birthday! (sorry is a bit late :c )
Second of all, you’re not “highly sensitive”, you’re in your right to feel how you feel. I see emotional people being just a bit more “human” .
Now to answer your question: no, you’re not in the wrong and not ungratefull. The goal of having a birthday is to remember the accomplisments of each year, to remind us and our loved ones we are alive, well and going strong. So obviously you would want at least a “happy birthday!” or a hug for example. I’ve been what you gone through, however I was a bit more lucky since the blah members wished me hb and my boyfriend did aswell. But I know how it sucks you go out and no one says anything, you expect at least a text , someone to remember. However I realised sometimes people are either busy with their lifes or .. sadly don’t care. If your case is people not caring, I suggest you trying to find new friends. In the case of your gf tell her how it means to you. Take your time, take a deap breath and explain her in a calm voice how much would mean if she cared a bit more.
I hope that next year you’re still around btw so we can all wish you a happy birthday, and hopefully your family and friends will be nicer. You deserve all the love in your special day