Hello,
Pregnancy chances are nil in your case because ultrasound is the most specific pregnancy test and it has not shown any pregnancy in your case. Frequent urination can be due to many reasons which can be physiological or disease-related, and include excessive intake of liquids, diuretic substances (including tea, caffeine, alcohol, certain drugs), anxiety, exposure to cold, diabetes mellitus, diabetes insipidus (central or nephrogenic), urinary tract infections or obstruction, etc to name a few more common ones.
I hope it helps. It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.
You're not pregnant. Fifty home pregnancy tests are pretty hard to fool. Please don't obsess so much.