Leviticus 11 - God calls His people to live holy lives which includes their diets. They were not to eat any unclean food, that is, food that could cause disease or would just make them sick. God explains what animals are good for food but details the animals, fish, and birds which they must not eat. (A side note here is that the translation of some Hebrew words into English is not always easy and straightforward. Some Hebrew description of animals presents a difficulty for some translators to know exactly what animal may be referred to). God also warns against touching the bodies of these dead animals. They might carry disease, so the one who touches them must bathe and stay away from the camp until evening. Note that God makes very clear that He wants His people holy because He is holy. See verses 44,45.
Leviticus 12 - This chapter deals with purification after childbirth. There is no reason to think of conceiving and giving birth to children is sinful. But God wants His people, mothers in particular, to have time to heal from their pregnancies and to spend time with their children, twice as long with her daughter who is being brought up in a male-dominated society.
Leviticus 13 - Infectious skin diseases can not only harm the person who has them but they can spread. The person who is so affected must allow the priest to examine whether the rash or wound is really a disease spreading infection or if it is just a scab. The person so afflicted must do what the priest says including staying away from healthy people. This idea of isolation is similar to our understanding of quarantine. This is still practiced today as a safeguard against spreading disease. The term "leprosy" in some translations is better understood as a spreading skin disease that could be leprosy or something similar.