Have Very Irregular Periods, Trying To Get Pregnant. What Should I Do?

I have very irregular periods, I actually have not had a period since July. My husband and I are trying to get pregnant so I have been tracking my temperatures so I know when I am ovulating. I am a 21 year old caucasian, weighing about 120 pounds and 5 feet 5 inches. My temperature has been up for about 20+ days and it has been at 98.1 (or slightly higher) for about 5 days, which from what I understand means that I am pregnant. I feel some of the normal symptoms, dizziness , fatigue, nasuea, my face is breaking out, which only ever happends during my last pregnancy in may which ended in miscarriage about 6 weeks along. On the 11th-16th I started lightly spotting brown blood . I have NEVER had a natural period like that, it is usually very very heavy very painful nothing like this. I have taken a pregnancy test on Sunday and it was negative, I used a more sensitive one today and it was still negative. My temperature is still up, and my gut feeling is that I am pregnant. What s going on? (I have been taking prenatal vitamins since January, I also take cranberry pills and ginger capsles, and use a progestrone cream twice a day.)