Hopefully Claritin works for you, it didn't for me. And to answer your main question yes just fluid can cause ear pain. Keep an eye on the pain. If it gets bad see your doctor for infection, and if behind your ear gets really sore and turns red or purple run, don't walk to your doctor. That usually means the bones in your ear are infected. It's rare but does happen ( did to me ) usually fluid will clear up on its own with no issues but after 3 months if it's not moving you will need to see an ENT and possibly have the fluid drained via a myringotomy. Good luck!!