Even tylenol, you would not want to exceed 2
or 3g per day. Basically, ask you hepatologist about any medications you are taking, including OTC's.
Allergies themselves can cause much headaches because the sinus system in the areas behind the forehead, nose, and eyes are clogged up with fluid. Ask your doc for a safe allergy treatment. For myself, I sometimes use a decongestant for the bad allergy headaches.