What Causes Headaches And Missed Period While Breastfeeding?

hi I just had a baby 7 months ago and I havent had sex since then but I have a bruise on my arm that I cant explain and no period for about 2 months, nautious and headaches every day. I breast feed my daughter and Ive also been getting dizzy and light headed a lot and Ive always been very skinny and cannot lose the weight from my daughter do yuo have any idea what this could be.Also I had a c section