I really hate to tell you this, but I think it goes with the territory. Happy Birthday by the way. Adult Children are very self focused and busy with their lives. You are actually lucky that they think of you at all, because chances are they don't. This is the beginning of their lives, careers, families and you are no longer the needed mother. You are a pillar for them, an example for them to navigate older age. This is a hard pill to swallow. The older you get the more you will be in this category. The best thing you can do is cultivate your own life, your own friends and thank your adult children for what they gave you. It does mean something to them. I would not complain, nobody likes complainers when you do something you think is nice. If you dislike them so much (can't imagine - but each to his own) then make a point of bringing them to a care home and asking the staff which resident would enjoy them the most. I'm 62 and don't want any more 'things'. I ask my children for something I can eat or look at and toss. Before your birthday arrives you could have lunch with your daughter or son and say how much need a scarf or a toaster - I don't know, whatever you think you want. Just mention in conversation, not that you want it for your birthday. Life is way way too short to be disappointed you get flowers or candy. I would ask myself what that says about my life rather than what it says about their lives.
Just saying.