Raisin,
Try not to be so hard on yourself. What you experience with losing sight of what techniques you want to use is pretty common, especially when you are fairly new to sparring (my definition of new is < 2 years of active sparring).
I'll be the first one to tell you that I've gone through this myself, and still do from time to time. Nothing disrupts the thought process like getting hit.
Unfortunately, the only advice I can offer is to keep working at it. The best way to do that is to keep sparring. I agree with others to use basic techiques and just work them.
If your sparring with senior students, definitely take stock in the small victories. If you can land shots now that you couldn't a week or month ago, that's a victory. You don't have to win to improve. You just have to continue to be willing to try to improve.
Sparring does not necessarily become a natural thing to all people. In my school, I've seen many people that are great at sparring, and many people who are not. I'm 34 years old, and I get schooled time to time by some of our younger students and some of our older.
When someone beats me, or I have techniques that don't work, I try something else. I also spend alot of time working on techniques and combos at home. Nothing can replace the actual experience of trying those techniques while sparring. Timing more times than not is everything. Once you learn to set up a technique and you gauge the reaction time of an opponent to how you throw a technique, you skills will improve.
The other thing I can say is that with time, once you are more accustomed to being hit, the more you will learn to keep your cool, and remember techniques. The person that maintains their cool in the bout will generally win if skills/weight etc are equal.
Hope this helps a little.
Sincerely,
Thomas Kangas