First Response Pregnancy test 3 positive 3 store brands that were negative HELP?

I testes with 3 first response tests and all were positive, kinda fainter but defiantly still there. so then i tested with a cheep o, and it was neg. Then I went to the women s clinic, and they tested me and it was neg. but then again that was using a cheep o, that was on Monday, so yesterday i went and found the same test they used and again it was negative. My breast are not sore, and I haven't had any spotting. I am close too a week late, i have felt like i have had cramps, and this is the sixth day of that. Maybe a little bit nauseous, and i get light headed with headaches but i don't know if that's my mind making that up maybe the first response just tested wayy early or the were false? I just dont understand..I know they only show up if there's HCG, but then why wouldent the others. I first started testing with the FR like a week and three days ago. help please!