What Causes Weight Loss,chest Pain And Absent Periods After A Delivery?

I am 27F, with two children 7 months and 3 years. Since my last child I have been losing weight and hair. More than common. I have yet to have my menstral cycle return. I have been extemely tired and on edge for the past couple months. Now, I have been having chest pain, a dull sqeezing pain in my chest. I've noticed that diring time of chest pain my HR is around 60. My normal HR is around 75. Could this all be related?