Why does the first covid vaccine give us sore arms (in some people) but then the second dose is harder to get through with flu like symptoms while others don't have much symptoms?

The sore arm can be from the needle piercing skin and then entering muscle along with releasing liquid into the muscle. Antibodies against the vaccine develop and following the second vaccination 3or4 weeks later, those antibodies are stimulated causing release of inflammatory substances which cause flu like symptoms more vigorously in some rather than other people. Young people tend to react more