BFP now BFN????

Stephanie
I got a vvvvfl on a boots own test on Monday (day AF was due) so I tested yesterday morning with a FRER and I got the faintest positive! I was so happy and told myself I would do the other FRER stick on Friday. But I couldn't get myself so I bought a cheapie from home bargains and did it this morning. Outcome = negative?!?!
I had a chemical a couple of months ago but I didn't get this many positives before it? 
Advise would be appreciated x