What Are The Early Signs Of Pregnancy?

I have been having lower pains in my pelvic area, started about a week and half ago. When I would go to the restroom and urinate, it wouldnt hurt during urinating, it would hurt afterwards. It was like I had alot of pressure on my bladder. I have been really fatigue the past week, also. I went to the dr. he did an ultra sound and said that the thickening of my uterus was really thick, and just told me to take a pregnancy test yesterday. So I did, it was negative. So I called him to tell him the result, he advised me to wait till after Christmas and retake test. My cycle is due mid of next week, So I know its early. We have been ttc for the past 5 years, havent had any luck. So is this a good sign that we might be pregnant, or could it be something else?