I remember the first time a birthday really bothered me, and I was much younger than you. Funny thing is that birthdays became real celebrations for me once I retired. Do something special for yourself, even if it's just taking time to watch a sunset. Aging does bring aches and pains, but not everyday is bad and there are many things that bring relief. Eat healthy, get some exercise that you enjoy at least three times a week. I found that using a chiropractor and an accupuncturist helped when I had back problems. Do what works for you.
If it's ok with your mom, speak with her doctor. Then you'll have a much better idea of what you can do that will be helpful.
Enjoy your daughter each day for the next two years. By the time she is ready to move out you will be more ready to have it happen. It will be an adjustment, just like everything else in life, but because you will have had time to think about it, you'll have some ideas about what to do with any free time you have.