I feel really guilty asking my parents for gifts for my birthday...?

Well, to start, you should examine your own way of thinking that leads you to act that way. Is it just a route that you've gone towards to keep from getting too close? Are there doubts in your mind about their love for you, or feeling smothered?

If so, try to think about how you would want to be treated, and what you really want in a moment. Stop to think about how you're feeling, and imagine how they're feeling.

That's just to work on the relationship. For gifts, I find it easiest to make a list of things that are easy to find, and fairly inexpensive, that you want, but you don't want to get for yourself. That will simplify the whole affair, and let them know that you don't care as much about the cost of the gift as the thoughtfulness behind it.

Love/ hate relationship.

Tell them you want nothing more than to sit with them for dinner

if you love them then they should love you back