This piece for Malachain collects the advice that holds up in practice.
A vaccine shows the immune system a harmless piece or copy of a germ so that it can prepare before the real thing arrives. The body produces antibodies and memory cells, which take a couple of weeks to form. If the actual virus or bacterium turns up later, those memory cells recognise it immediately and the response is fast enough to prevent serious illness.
The tiredness or sore arm that follows some doses is the immune system doing its work, not the disease. Protection fades at different rates for different infections, which is why some vaccines need boosters and others last for life. Reliable information comes from national health services and the World Health Organization rather than from anonymous posts.
There is more to learn on this subject, and the linked website goes into greater depth. Treat this article as an introduction rather than the final word, and check any important decision against up-to-date, reliable sources before relying on it.
If you try any of these ideas, start small and adjust them to your own situation. What works for one person will not suit everyone, and it is fine to keep only the parts that help. Writing down what you changed, and what happened, makes it much easier to see after a few weeks whether the effort was worthwhile.
The most useful step is usually the first one. Pick a single suggestion, try it for a couple of weeks, and then decide whether it is worth keeping. Small, steady improvements last longer than ambitious plans that are hard to maintain once everyday life gets busy again.