Normal vaccination reactions
It is normal to have certain reactions after a vaccination: There may be redness, swelling or pain around the injection site. Fatigue, fever, headache and aching limbs are also not uncommon in the first three days after vaccination.
These normal vaccine reactions are usually mild and subside after a few days. They show that the vaccine is working, because it stimulates the immune system and the body forms antibodies against the infection that is only "feigned" by the vaccination.
https://www.dw.com/en/covid-19-risks-and-side-effects-of-vaccination/a-56136620