Seeing things

Ok so I have tested @15 DP IUI or 13DPO (if you go by my chart lol.) But I swear my eyes are trying to mess with my head (or vise versa) Becuase I will see "something" of a line at one angle and then nothing 10 seconds later at another. Grrr I hate this. Why can it not be a clear cut answer (and no I am not spending over $20 for a digital, when I can get 3 sensitive tests for under $12!).