After surgery you must have been advised some orthoptic excercises. If you have not done these exercises, you are likely to have the problems described here. You should get in touch with you surgeon and the orthoptic department who will do the needful.
Meanwhile, you can use some anti-inflamatory drops in the affected eye to relieve the symptoms of pain and if headache is intolerable, you can take some analgesic
tablets as and when required.