Check the sensitivity of your test. The box should either say how soon you can use it (first response - 3 days before period is due) or it will have something like 50iu/l or 20iu/l (international units per litre) the lower this number - the more sensitive your test is.
I'm 6w 2 and still find it hard to believe so I did my own little experiment the other day with a first response test.
I dabbed on test into my urine but not enough to properly wet the tip (this was an accident on my part

) and decided it was a "wasted" test so I dipped it in some tap water - to help the urine along the stick, but I also did a control and dipped the other (2 in a box) in just tap water.
The one with a teeny tiny bit of wee(and water) gave a positive while the water only gave a negative (thank goodness

)
give it a few days and then test again - you may find it easier to "catch" your wee in a clean container and dip the test into this instead of trying to hold it in your "stream" - especially if you are a larger lady like one-self :d