What Causes Delay In Periods,weight Gain And Pain In Abdomen And Back?

I am a healthy 26 y/o female trying to conceive a child with my fiance. My last menstrual cycle began on April 13th and was abnormal, only lasting 3 days and with extremely light flow. I am now 2 weeks late for this month's menstrual cycle and have noticed the following changes: Fatigue, restlessness, weight gain, slight nausea, abdominal pain, and lower back pain. I have taken two home pregnancy tests. One of which was 3 days ago and another this afternoon, both of which have come out negative. Is there still a chance of pregnancy?