Hello welcome to Healthcare Magic.........
Sorry to know about your miscarriage
Miscarriage has several reasons, u need to understand this. In majority its the natures way of aborting a defective baby. In few there are other resons.
All you need to know is that it was not any of your fault and that it would be ok with time.Ultimately we donot have control over few things and so no use brooding on such things. So though its really stressful to deal with you need to stop thinking of it all the time and start moving out and becoming social.And dont worry the miscarriage would not affect your chances of further becoming pregnant.
2) About the pain and the cramps- it seems it was an incomplete abortion
and so u can consult a gynaecologist and get a dialation and curattage done to clear if any products of conception are left behind.