TW : blood clot - What on earth is on my pad?

I had endometriosis excision surgery 3 weeks ago and they fitted the marina coil. Stage 4 Endo was found on my bowel, uterus and near my ovaries. I’m having my first period since the surgery (it’s painful, still kinda heavy and I’ve been bleeding for 9 days instead of my usual 4 days) and I’m not sure if it’s because of the surgery or the coil but this was on my pad. I’m not normally one to ever get blood clots and from googling it looks slightly like the Uterine decidual cast) is this normal?! I’m worried 😫