Nothing bad. If the jab you are talking about is Depo Provera, it is just progesterone, which is normally present in the body anyway. In some countries it is given to a pregnant woman who has had a history of miscarriage because it helps the pregnancy to progress well. By the way, it is a good choice of contraceptive after childbirth because it helps the mother's milk supply.
It's possible to be pregnant, on birth control, and not know it. If so, you'll just stop the birth control when the pregnancy is discovered.
Nothing
If the birth control fully works, there won't BE a fetus, birth control will do nothing about an impregnated egg or the baby that it will result in.
Birth control is what is used to prevent unintended pregnancy, there are multiple different types of birth control that work in different ways, it is ignorant to say 'birth control' to mean one specific type of birth control. Without knowing what type of birth control you're referring to we cannot answer your question - some birth control does absolutely nothing to your hormones, some birth control completely shuts down your hormones.
Birth control loses all of its effect the day that you stop using it.
any pharmacy no age
You can get pregnant
There is no increased risk of pregnancy if you miss the non-active birth control pills.
Yes. In the first few months of being on birth control, this happens frequently, and it fades as you continue to use it.
Nothing
Yes, but be aware they might find out sooner or later, and even destroy your birth control if they're selfish or even violent. No matter what kind of relationship you have with a man, if he says no to birth control, dump him!
Sperm is not affected by hormonal birth control; it does the same thing it does if you're not on birth control, except that there's some decrease in how much sperm can get into the uterus (due to thickening of the cervical mucus). Hormonal birth control affects the egg.