Im 26 Just Had My First Period After Missing The

Im 26 just had my first period after missing the last 2 months . i passed a grey like tissue along with heavier blood clots then usual no pains just slight aches ..the only time this happened was 2 years ago when i miscarried , i did a pregnancy test before the period which was negative ,so if its not from a miscarriage why have i passed it and is it anything to worry about?