Explaination Please

Now I might seem like an idiot but I promise I’m not. My last period was December 19-24th. I have not had a period since and my period is every 31-32 days very consistent. Throughout January, I have been experiencing the back pain, stomach cramps, exhaustion, sore breasts, mood swings, dehydration, pain during sex. I thought it was my period it never came. I’ve been taking tests Equate, Clearblue, Clearblue Digital, and First Response. They were negative all of January. My last negative was Friday morning the 10th. I took 3 February 16th and all three different brands and styles were very positive, showed up immediately. I meet with my doctor Wednesday to get an actual estimation. But until then, can anyone explain how I’ve missed 2 cycles but took nearly 8 weeks before a positive?