Is it normal? I'm 18 years old, I have a tooth eruption, the dentist says, and he further claims that its not the wisdom tooth! Its painful....

Everyone's DIfferent. Permanent first molars tend to erupt into your mouth at about 6 years of age, second molars at about 12 years of age, and "wisdom teeth, " or third molars at about 18 years of age. But there are instances where teeth can be delayed in eruption due to other teeth being in the way, or you can even have extra teeth. A dental examination with x-rays can confirm what is happening, and help you find trea.
Ouch! If it's the 7th tooth back, it's probably 12 year molar. If 8th tooth, probably wisdom tooth. Eruption patterns can vary widely. People with congenitally missing wisdom teeth often have delayed 12 year molars. Eruption can hurt (why do you think infants cry), so ask your dentist for suggestions to take the edge off.
No but. It is not unheard of... Obviously without seeing you it is not possible to see for sure...The tooth could be erupting late... Normal 2nd molars usually erupt around age 12. Talk to your dentist about the pain if it continues..
Yes. Very likely wisdom teeth. You need to visit a dentist for examination and receive a panoramic examination to determine the source of pain.