I've miscarried twice in the first trimester with no d&c needed. If you were "blocked" You would be experiencing pain and signs of infection- fever, cramping, etc, and if it's been more than a few weeks since your miscarriage, these signs would be severe enough that you would have sought med treatment. Your cycle might still be sorting itself out, or your 1-day period could have been implantation bleeding from a new pregnancy. Wait a week, test again, and if it still comes up negative than your cycle might just be irratic still. With my first mc, it took my cycle about 2 months to be regular again, and you could set your clock by me. With the second mc, i also had a bladder infection that moved to my kidney and messed me up down there for months.
I also had this problem after my mc ( no d+c needed) however my periods have since straightened themselves out! However are you still getting clots/ bad pains as that is what I have been experiencing which has made me worry