What Causes Irritation And Nausea After A Miscarriage?

i am 22 i had a miscarriage at 20, i have had a sore back that has continually gotten worse over the past 4 weeks, i have had mid-cyle spotting ( a dark brown thickish spotting) for the past 2 months, i feel nauseous and i am irritable, i am hotter than usual in bed and find it difficult to get comfortable, i did a test 4 weeks ago that came back negative and 1 a week ago that also came back negative, both were taken mid afternoon, please help i do not no what is going on with my body?