i'm a 20 year old woman, and for some reason i havent had my period

If you had one positive test, you are pregnant. False negatives are very common with home pregnancy tests. 

As far as your doctor appointment, they will do a vaginal exam, want a urine sample and some blood tests. You will be weighed and given a TON of information to look at. You may be given a prescription for prenatal vitamins, if not just get some from the vitamin section of the drug store. No one brand is any better than another, unless they make you nauseated :)

For the nervous boyfriend, remind him to breathe. Sometimes a few deep breaths and some reflection will help. Remind him that babies are born everyday in to families who were not planning for them and things usually work out fine. :)

Good luck with everything :)