Flu shot? And weight?

So

I have never in my life had a flu shot and my doc wants me to get one, a common suggestion i guess. Im 19 weeks. Just worried how/if it will affect me and baby since my body is not used to getting any shots?

Also i got weighed today and ive gained nine lbs! Is that a lot for 19 weeks??

Thx for any advice🤰🏻