What were your cycles like before your miscarriage? I'm not sure about the others but mine went right back to 24-26 day cycles after my miscarriage and after Wyatt.
I found a website that gives you when you should test.
http://www.fertilityplus.org/faq/opk.html
Hopefully that will help.
Edited to add: I would use your shortest cycle prior to miscarriage. That way you won't miss it!!