You may not OD, but you may get a tummy ache if you take the excedrin too soon. Trust me. I used to get headaches at least 3 or 4 times every single week. No joke. I'd wait a little while and depending on what type of headache it feels like, I'd lay in bed and either put an ice pack on it or a heating pad. If it's a sinus headache, heating pad. If it feels more like a migraine, ice pack.

Then if that doesn't help it go down, I'd wait a couple of more hours, then make sure you eat something before taking the excedrin.