welcome to HeathcareMagic
are due to hormonal
imbalance;anaemia;thyroid problems ovarian cyst
etc and less bleeding during periods can be due to anaemia for which you are on treatment.The pain in left side of abdomen can be due to inflammation in pelvis;constipation;even a ovarian cyst.So please get a ultrasound
done to find the reason and then get treated accordingly.Please consult a Gynaecologist for opinion and treatment.