Likely no. It really depends on "excessive." brushing twice daily is good. Brusing 3 times a day (after lunch) is great. Anything beyond that is probably "excessive" and not necessary. Flouride in the concentration of toothpaste is safe as long as you are not swallowing it. If you are having tooth ache related to "excessive use, " i would presume you are brushing too hard and causing abrasions - see a dentist.
No. No, see your dentist for examination.
No. The Fluoride in toothpaste can not cause a toothache. There has to be something else going on. Please see your dentist.
Not really. You would have to have eaten (swallowed) an insane amount of toothpaste while your teeth were developing to have a problem such as this, in which case you would see some pretty remarkable changes in the tooth (dark brown, malformed, discolored). I would look for another source of the tooth pain.