Rear derailleur malfunctions
Glad you are having fun on your bike! Here's a link to adjusting the rear derailleur -- it's worth a look if only to gain some insight into the RD's settings and perhaps what might go wrong. OTOH, you might be able to fix/adjust it yourself :)
https://www.parktool.com/blog/repair-help/rear-derailleur-adjustment
Before working on the RD, it's a good idea to at least brush off any dirt/mud/stuff that might be on the chain and gears. It'll be easier to see what's going on, and the problem might just be something stuck in the gears as with your first issue.