2 missed periods but negative pregnancy tests!

Has anyone else experienced this?? Missed mine the 21st of last month and 4 days ago! Since missing the first one ive been crampy, icky feeling down there, 2 weeks after the first missed one i had a tiny bit of light pink brownish spotting but only one time when i wiped after going to the bathtroom, peeing at least every hour, constipated, irritable and moody, swollen breasts, but still negative! Im so frustrated and my doctor doesnt have an opening for another month