‼️⚠️ TW: possible miscarriage question

hi, i hope this is the right group to ask this in. and i am not trying to be insensitive at all, i know how difficult a miscarriage can be, as i have miscarried in the past.

i think i may have just had a very very early miscarriage. im not sure if i was pregnant or not as my periods are irregular, i was having a few pregnancy symptoms and i didnt test or anything (im also breastfeeding currently). but i started having horrible lower back pain and my lower abdomen was tender to touch, with some cramping . i assumed it was kidney stones, but today i was using the restroom and passed some small pinkish tissue, and i havent stopped bleeding since. My question is how can i confirm a miscarriage? thank you in advance