RSS feed doesn’t update when post published

Hi,
I had some issues last week with >my feed not showing correctly. I thought it was a cache issue that got fixed. But i am having the same problem again.
The last two posts published on my website are not showing in the feed. (March 15th & March 20th posts. According to the feed validator, the last post that shows in the feed is March 14th). It looks like the feed validates though. I am not sure what the issue is and how to fix it.
I appreciate your help!
Thanks!