What Are The Side Effects Of Iud?

I am 24 years old. Had a baby one year ago. I have an IUD ever since the IUD ive not had a normal period and when I do have it they last up to 3 weeks off and on but the whole time my period is black.. is this normal? I am under stress half the time. I am a single mom to 2 kids, full time job, and i go to school. could this be the cause of that?