missed my period, but negative tests

hi! i just wanna start off that im not trying to get pregnant but me and my partner are in any case excited if i am. im a bit on the underweight side but i eat fine and get alot of exercise. im also anemic and have a vitamin deficiency and my periods are never consistent ( i have pcos ) but i havent missed a period in about a year. last month mine came really late on the 26th ive taken 5 tests so far ( i took abt 5 tests so far) i took a dollar tree about one about 4 days afo which came out negative , i took two yesterday one in the morning and one in the night which both came out negative and two right now which are all the same brand (pregmate) and everything has been negative so far! has this ever happened to anyone else before? should i try a different brand and wait a couple more days?