I have found that 1 or 2 affirmations work best for me. Done usually as part of my early morning routine and before sleeping when going to bed at night. If you affirmations are too specific and on too many topics and repeated too often it is easy to see how your head would hurt.
Affirmations should ideally be True, but not specific enough to be unbelievable. I teach that you should feel better as a result of doing affirmations. I would have said they should be open-ended statements but that would be too broad.
If you find that you are doing many affirmations on many topics then consider combining the topics in a broader/ more inclusive topic. Set aside some quite time to do your affirmation once or 2x per day. Affirmations should set your mind in alignment with desires ( or should I say, stop your mind from preventing a manifestation) … your job then is to allow. 🙂