Happy birthday, Ardenrose. :) I don't know about you, but I'm often depressed on my birthdays. Though, to be fair, I've had a couple more than you.
I'm sorry that you are in pain. Just remember - you are not your illness, any more than you having a broken leg would mean that you are a broken person. It's just a thing. A thing is a thing, not what is said about that thing. BPD sufferers tend to be sensitive - this is not bad. I get sensitive teeth sometimes - that's an easy fix, I just use sensitive toothpaste, and maybe avoid hot and cold foods for a while. Can you try to avoid the things that you are sensitive to? This can be situations, but can also be certain people.
I don't know you, but I promise you - I care. You are a person. You are a living, breathing human being. That means that you are worthy of compassion and kindness, at the very least. I'd bet that you are worth a whole lot more than that too.
Today is just a day. I think I get depressed on my birthday as I want it to be more than it is. But it's just a day. Tomorrow is a new day. They do get better.
Please keep in touch, and let us know how you are doing.