Had D And C Procedure After Missed Miscarriage, Small Clots On Body, Back Pain, No Periods Yet. Reason?

hi, i had a d and c procedure on 28 Jan after missed miscarriage. i had a just a few days of bleeding. about a week later i suffered with severe abdominal pains and went back to hospital. they carried out a scan and said i had some small clots my body was trying to expel and gave me some antibiotics. 6 weeks after the d and c, i had 4/5 days of very dark discharge but nothing of colour or flow of normal period. for the last two weeks (weeks 10&11 post d and c) i have experienced lower back pain and some pelvic pain but I've not seen my menstrual cycle. i have tested for pregnancy yesterday but it was negative. my period was due this week. why have i not yet seen a menstrual cycle? we so want to get pregnant again but it is difficult because we are unable to work out ovulation dates.