Whats going on with me? can anyone help!?

ok I had my period on March 16th and then around march 28th my husband and i had . for one whole day on march 28 my left side of my stumic hurt and now i'm feeling sick 24/7, going from hot to cold, my lower back has been hurting me for 3 days now. I know i'm not going though early menopause because I'm only 21. What is going on? Could all this be in my mind or could we caught it? if we did finally catch it how soon can i test?