Is it possible I could still be pregnant?

Today I am maybe 14-15 DPO (not completely sure, but from body signs) and I have been testing for the past 4 days and I have always had these really really faint positives tests, but they never get any darker, leading me to believe that they were false, or my mind was playing tricks on me. I have a normal 30 days cycle, like clock work, and today I am suppose to begin my next cycle (really don't want to, as I am TTC) I have heard that sometimes it takes longer for the HCG to produce adequately in the urine, so some women don't test positive til later on in their pregnancy, but for me that seems a little impossible because last time I was pregnant (In June) I tested 4 days before my missed period, and got a HUGE bfp. I unfortunately miscarried that baby at 6 weeks. I just think that I may be out this month, but I know that until my period shows, I am still in the running. But it confuses me on why I wouldn't get a dark bfp by now. And the light BFP's that I have had are way too light for me to want to trust. Like it's something that you to look at closely to see, so I don't believe them because if I were pregnant, the lines would have gotten darker by now. So what do you ladies think?? Is there any chance I could be pregnant?