Please tweak

Jenay • I`m 23 my husband is 33 we have been married for almost a year I have an 8 year old son. My husband and I have been trying to conceive for over a year
I'm 15 days late this is my 4th test the first three were all negative could it be because I'm using dollar tree tests ? Has anybody repeatedly gotten negative with dollar tree tests then get a positive with a different brand?