When to start OPKs?

Rebecca • My hubby Mike and I have been married for 3 years. We welcomed Isabelle on 2/15/14 and are expecting baby #2 in 9/16!
Hi everyone! I'm just curious when I'm supposed to start taking OPKs? Sorry if this is TMI... We miscarried twins on 8/8, and my period started on 9/9; still bleeding, but it is getting lighter every day. Glow is predicting my fertile window to be around 9/24-9/28, so I'm not sure when to start testing (we didn't use these with any other pregnancies). Thanks in advance!