Hi Danielle!
With nursing, that does make this a bit more difficult. The first herb that comes to my mind would be cayenne. The safety during nursing is unknown, so maybe do some research on it and see what you are comfortable with as far as internally. Some babies are more sensitive than others to spicy food in general, so that is another thing to think about.
Sometimes, herbs that aren’t safe internally while nursing can be safe topically though. Perhaps a cayenne tincture used on the skin above the area of the clot might help dissolve it? Again, do some thorough research before trying it. Also, check into topical castor oil. I haven’t read of it helping with blood clots specifically, but a lot of people swear by it for breaking up other cyst like problems. Hope you find something that works for both you and baby!