We are sorry to hear of your miscarriage.
You are permitted to perform a hefsek taharah as soon as you feel ready for it. Clean yourself well internally beforehand, as by soaking in a bath, to minimize interference from residual spotting. For this cycle, you may omit the moch dachuk.
If you are uncertain about the color of the hefsek taharah or of another bedikah, please bring it to a halachic authority for evaluation rather than assume the clean days cannot start or have been invalidated.
A stain found on white undergarments during the clean days does not invalidate them as long as its size is smaller than a gris (roughly the area of the American dime or Israeli shekel). Larger stains can also be evaluated for color as necessary. Please see our article on stains for more details about staining, and please contact us if you have any trouble getting through the clean days.
Mikveh immersion is permissible as soon as you finish the clean days. (The exception would be if both the major part of the tissue did not pass until the D&C, and the D&C took place over forty days from your last mikveh immersion. If that is the case, you should not immerse prior to the fourteenth day following the D&C, even if you complete your clean days sooner. Our article on miscarriage discusses these halachot in more detail.)
We wish you a refuah sheleimah. Please don't hesitate to write us with any further questions.