Why am i suffering these terrible pains is it the new pill?

i have just changed from cilest to yasmin. it is my fourth day, but i have experience severe uterus pain.and the some mild chest pain. but a week before that i had missed a pill. i can not figure if the bleeding on the monday was from a cut from my partner or spotting. im am freaked out. as this is the first time i have changed the pill, and got these pains apart from abdominal one i have had for the last few months which have been checked on by the doctor im doing my head in can anyone help