Hiya I know what your going through!I went through the same thing!I missed a period and did a hpt,actually I did 2!They both came back negative so I put it down to stress!Then 2 months later I still hadn't had a period,i eventually went to the doctors and found out I was 16 weeks pregnant!I was expecting it but still shocked!I felt like I wasnt ready and wouldnt be able to cope but my baby boy is now 6 weeks old and I am coping fine!
Ramble over, I would suggest that if you dont want to go to the doctors then wait a while and do another hpt, but remember that they are not always 100% accurrate, so its best if you do go to the doctors.
Also if you do find out that you are expecting and you are positive you dont want it then you could have an abortion or put the baby up for adoption, but you will be amazed at how much support you will get so remember that you are not alone!
Keep me posted and pm me if you ever need to chat!
Take care,cath