Does Missed Period And Cramping In Lower Abdomen Indicate Pregnancy?

I think I might be pregnant. Last month my period was 8 days late, and only lasted a day and was more of a spotting. This month I didn't get my period and I'm 2 weeks late. I have taken 4 pregnancy test, all different brands and all of them done in the morning. I also made sure to pee in a cup and dip the test. Three of the test came out invalid and one negative. I have also had a bit of weird cramping in my lower abdomen. Is it possible I could be pregnant? I'm 20 years old, and weigh about 165.