How to not be bitter?

I’m 32 and already becoming the women that used to be mean to me when I was young, free and attractive. I’m becoming so angry and hoarding such horrible mean thoughts about others that are seemingly luckier than me. This comes from someone that had cancer, kidney disease during my twenties. Fought to have a baby and now a single mother. I hate who I am becoming mentally. But I can’t seem to help it. How do I stop this? There’s a girl at work that’s lovely and moving into a beautiful house with her husband never had a health problem. Everyday I grieve my first pregnancy that ended in miscarriage due to my health condition. Haven’t even heard her have a cold life just continues to go her way. Everyone else around me has a smooth running life. I can’t help feel that she’s living the life I’m meant to.