Hi.I was on my 7th day menstrual when I felt a sudden pain on my left uterus area?

Then I felt sumthing solid came out so i went and n check its kinda look like chicken fat but thicker and there is small dark blackish thick blood on it..its really painfull before i feel it coming out and my back ache so my knee hurts till i could not stand properly and i have to bend before it came out.currently i suffering from minor slip disc Usually I only have 3-4 days max during mens but this time it much longer.and i seldom feel period pain .first I tot maybe due to the painkiller I took.I'm not sure whether it's related but the solid thing dat came out really scares me..wondering if it's tumor or sumthing..