Thank you for reaching out to us.

Abstaining for a day or so when there is staining that does not make a woman niddah is not a halachic requirement, but rather a recommendation to avoid having a flow begin during relations. Since the woman is not in niddah, relations are permissible. If a woman is reasonably confident that a flow is not going to begin, or that she is not actively staining at a given time, then she can make the decision to go ahead with relations. (Some women wipe externally with toilet paper, not immediately after urinating, to get a better sense in the moment.)

Before having with relations when there might be staining, it is especially important to take precautions to avoid becoming niddah. See our discussion of relevant precautions here.

As far as the second part of your question: So long as what you have been experiencing is staining rather than a flow, the idea that relations may be somehow triggering it is not of halachic concern. However, we would suggest seeing your physician and confirming the Mirena is properly in place and that the strings are of optimal length, on the chance that this is somehow related to what you've been experiencing. You can also discuss medical possibilities for addressing the staining.

Please let us know if we can be of further assistance.