Mazal tov on the birth of your baby!
We follow the view that a woman is permitted to use contraception to space her pregnancies. A mother’s healing and ability to care for her baby are halachic values. There is additional leeway for longer spacing when a couple already have a boy and a girl.
Therefore, based on what you write, you may use contraception for the time being. Learn more about the factors involved in permitting contraception on our site here and here.
With a diaphragm, you need a new fitting after each pregnancy. Please make sure to discuss this with your physician at your postpartum visit.
Please let us know if we can be of further assistance.