injection side effects?

A few days ago i had 3 injections to help prevent some illnesses... i had 3 cause i missed out on a few at school cause i wasn't in for them...

My arms were sore the next day... then the next day after i started getting really tired... i mean i do mixed martial arts and i thought it was from training cause i did push myself hard that day... and was very tired after...

So the next day after i felt absolutely tired :S... i had to do something that day... but i just couldn't go on... now today i feel really tired... i don't feel like i'm gonna throw up or anything... i just feel really sleepy and feel like i ain't got the energy to do things at all...

My doctor did say about all these side effects after i had the injections... so i know why i feel like this... but what i want to know is what is the best way to treat this?... should i just rest... take any medicine etc...?

thanks for any replies :)