Hi, my name is Teacher Gee. It's nice to see you posting actively here.

Dear, here are some corrections to the post.

I think it's something I ate this afternoon.

I thought really long and hard what I ate.

Probably it was some snacks so, I have trouble digesting now.
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I think it's something I ate this afternoon.
> (I think I ate this afternoon)  or

   ( I think there was something about what I ate this afternoon)

I thought really long and hard what I ate.
> ( I've been thinking about what to eat for a long time)      or

   ( I was wondering what I ate)

Probably it was some snacks so, I have trouble digesting now.
> (It must have been a snack, so I have trouble digesting it now.)

or to be more simple

>>>> I think I ate something this afternoon.
It was probably a little snack that caused indigestion.

HOPE IT HELPS! KEEP POSTING