1 month old (possibly) sick... advice

Ok so my 1 month old had a rectal temp of 100.0... my pediatrician said in the past if it hits 100.4 to take him to the hospital. I called the dr today due to his temperature and still haven’t gotten called back 😟

weird thing is an hr later I re-took his temp and it was 98.8. 🤷🏼‍♀️ I’m wondering if it’s possible the 100 temperature was because he pooped right beforehand.

He isn’t eating normal (but he is eating) & his sleeping is also off.

He’s very irritable and I believe he’s sick, my 4 year old was sick this past week with a fever & we did everything we could to separate them.

Thoughts/advice... how often would you be taking his rectal temperature?

Here he is yesterday right before he legit projectile vomited all over me 😅