still confused

i got pregnant back in november of last year and miscarried in january. my baby passed naturally without any doctors . but to this day i’m still confused on why i miscarried , i took care of my self , my fiancé made sure all my food was cooked properly and ate what i should . i’m also a type 1 diabetic but i took care of my blood sugar and insulin everything seemed all good . but we are thinking maybe secondhand smoke , i went to my mothers for christmas and everyone there smokes even around their kids which i don’t understand. but we came home and took a nap and i woke up and i felt like maybe discharge or something but i do have bladder leakage problems so i assumed it was that and i was bleeding like not a lot but a large amount than a pregnant women should expect . and it shorted down after a day so i assumed it was implantation bleeding but after the 1st of january. i started cramping bad and had bad clots , and then the next day i passed the fetus and bled for a few days . but afterwards my period started back after about 4 - 6 weeks , and i’ve been getting my periods normally . but i just want opinions on what you guys may think caused it bc we are still confused .