After misscarriage

Unfortunatly I lost my baby at 15 weeks last month and gave birth to Lucas on the 27th September, since then me and my partner have been having sex regularly without contraception, I had slight spotting 4 days ago which consisted of a small amount of pinkish blood only seen when I wiped, I have had no other bleeding since, what are the chances that I have conceived? And when would o be able to take a pregancy test to confirm that I have concieved? After the loss of Lucas my hgc hormone has gone back to 0 and done a test a week after the loss to confirm this. 
Thankyou xx