Diff brands have different levels. So it's understandable that you may not get +ves on some yet. I'd say used the brand that gave u the +ve and that one alone for now. Use it first thing in the morning (first wee after sleeping more than a few hrs) and see how you go. Tell ur partner not to drink too much before either as that will dilute the hormones and make the test less likely to be accurate. I have my fingers crossed for you and ur DP