What causes stomach viruses,someone Help!!!!?

i had nausea and diarrhea for 2 days with sore muscles,tiredness and weakness and the 3rd day was alittle better but felt some what out of it lightheadness now tonight my girlfriend is having the same problem what the hell is going on?Can it be ped on like a cold and can i get it again just by being with her like she was with me?what can be taken for it?Or have i been Hoo Doo.....