My Period Starting April 15th, I Did The "deed" With

My period starting April 15th, I did the "deed" with my husband sometime in the following week after and then I had light spotting on April 27th, accompanied with dizziness and nausea after I ate. Ever since then I have been experiencing extreme fatigue, cramping that lasts a minute & comes and goes, dry mouth & thirst on and off, a bit more constipated than usual, had headaches when I woke up 2 days in a row that last the entire day.

I took 3 pregnancy test, last day was May 8th and all came out not pregnant.

Could I still be pregnant?