Why is it possible to develop pregnancy symptoms while you are not pregnant?

My symptoms of which Ive had for two months now! Vomiting either early in the day or very late at night after meals, vomiting due to smells that rarely bothered me before! Headaches, Nausea, lower back pain, hunger and exhaustion after only being awake for 3 hrs. I am now starting to see changes in the size of my breast and darkening of my nipple area. And small light bleeding back to back within the past month. I have heard that some may develop this due to wanting to conceive NOT MY CASE! Which happens to be termed Pseudocyesis. Then there is ovum blight which is a miscarriage that will most likely go away on its own! The symptoms are lasting on and on. I have tested negative with the pee stick test approximately three times that of which one were taking at my doctor's office! I am not over stressed I deal well with stresses. I am up one pant size from what I was only one month ago! I also have these aching pains in my side. Is it possible that during my early 20's I am having an ectopic pregnancy? My doctor says I am very healthy from the results of my urine and blood test! I am not a drinker, smoker, I am in a monogamous relationship and have good Hygiene. I am trying my best to convince my brain I am not pregnant so my body can go back to normal! Today my face is actually glowing I don't know what is happening with me but I am not pregnant! Is there any other women who have had these same exact experiences?