Three months of only dark blood during period

[rx_harrison]

Over the past three months I have had periods that are completely abnormal for me. I normally get two to three days of bleeding with one heavy day with cramping and lots of dark red blood. Three months ago I started bleeding a week early with light brown blood and cramping for four days. Last month I only had a bit of dark brown blood instead of my normal period and this month I had a day of cramping with heavy brown blood and light the next day. I went to the clinic last month and they ran a urine test, took a swab and did a pelvic and transvaginal ultrasound. The only test that had some sort of result was that ultrasound they showed a mild benign thickened uterus. The doctor didn't seem too concerned and just told me to come back if the bleeding was still abnormal. As I had another abnormal period I went back yesterday and (as it is a walkin clinic) got another doctor. She was very rude and dismissive and made me repeat my situation three times and made me feel really stupid for being there (I read some reviews online that this particular doctor is generally rude and brushes patients off). I left very defeated and not sure where to go from here. I have been on Yasmin for 9 years so if this may be a factor I am switching from that to an iud. I have an appointment for the iud next month and hope that my body may adjust by then. Has anyone else experienced something like this?