Hi S potatoe,
Goanluv is right (calangute is very touristy), as are Baga and Candolim. All 3 resorts are within walking distance or a short taxi ride away. All 3 are populated by the Brits, it's nothing like going to spain though!!. You get a great cross section of people from all walks of life. Some backpacking and just passing thru, some longstayers (like me), who spend the whole British Winter in Goa, two week tourists who go out on charter flights and keep going back year after year.
Further North places like Anjuna and Vagator are also quite lively and are mostly populated by non-brit europeans, israeli's, swiss, dutch, germans. These resorts are more popular for their drug culture and parties, although the parties have now been banned and don't last 3 days like they used to.
The place that Goanluv mentioned with the co-co huts on the beach is very very nice but you'd probably only want to spend a few nights there because there are limited facilities entertainment wise.
South Goa is very quiet and mostly 5* All Inclusive resorts (not the best place for a girl celebrating her 18th)
Palolem in the far south is very beautiful and might be what you are looking for if you don't want too touristy or too British.
Most Accom here is in co-co huts on the beach, there are lots of good places to eat and some nice chilled bars. It is getting more popular now but you wouldn't have a problem finding a bed in November. Have a look at:
http://goa-india.com/palolem-beach.html
Have a great Birthday, Goldenflipflop