I'mI Am 24 Years.I Had Miss My Period For 3

I'mI am 24 years.I had miss my period for 3 months I keeping doing pergancy test and nothing show.I take primolut for 1 week and antiobic along wiy drinking epson salt thinking my period will come but after 1 week I find out I am pregant I went and did an altursound and it show I am 4 week pregant but the did see no heart beat omly de sac I am worried wheather to continue this pregancy