I have posed the question of tylenol vs ibuprofen, and people here have weighed in generally warning against ibuprofen. 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. But I don't have hep C and I am here as a concerned friend of a hep C person. I would ask your doc before taking med, including herbal med. There is a relatively new nonsteroidal nasal spray now (essentially an antihistamine).
Try some of the non medication measures for the headaches: warm bath (really helps with sinus congestion), massage, stretching excercises, yoga.
Wishing you well.
Typically, the docs told me to try Advil PM. I've taken a few hydrocodone (very few) over my last 18-weeks of treatment when the feeling of having been beaten all over my body with a ball bat comes along. The docs didn't freak out over it as they trust that I don't abuse them. Regarding the nasal alergies, which kick my butt from time to time, they told me to take Claritin.
you could get some allergra-D and nasal sprays for the pollen allergies, but i wouldn't risk anything stronger than tylenol.