Most people think that immune boosting is all about training and eating lots of vegetables. That is not all and in fact it is not enough. Your body requires much more than that. To build enough endurance, you will have to change your diet. There is no way that you will make it training like an athlete and eating like an ordinary person. You need a diet that is suitable for an athlete. You will have to learn the right way of combining proper diet and appropriate work outs.
One thing that you need to know is that bodybuilders eat big in order for them to get big. The bodies that you watch lifting weight on television is not built with junk food and snacks. It is achieved after taking several sizeable meals in a day. I mean more than that of an average person. If you are not noticing any changes even after training for some time, chances are that you are not eating enough quality and quantity food.
You have to feed your muscles with enough food. This is what will grow and build the muscles. It will also help you gain the extra weight that you require. Likewise for increased endurance levels and a stronger immune system, you will need foods and supplements rich in dim diindolylmethane that should enable you to workout longer and better.