What Do Shorter Periods With Pregnancy Symptoms Suggest?

Hi, I had what I thought was implantion bleeding three days before my expected period. It was a few drops of light red that was easily wiped away by toilet paper. I began to bleed three weeks later. During that three weeks, I ve had many pregnancy symptoms. Like, fatigue, bloating, cramping before expected period, acne which is weird, sensitive/tingly nipples, small bumps around nipples, and more hungry than usual. Once I got the bleeding, it lasted for three days, which my normal period lasts 4-5 days. I m usually always regular 28 day cycle. I took a few pregnancy tests during the three weeks I missed my period and it was negative. What could be the cause of this? I m not currently on birth control and my husband and I are currently trying for a baby.