Wifi Speeds under 10mbps for over 12 hours.

I had a full month of service with 0 issues when gaming, low latency, good connection and overall, nothing really wrong with the internet. We have the prepaid plan which I know needs upgraded, but that still doesn't explain how I can go from good enough speeds to play games with little to no issues to now youtube videos are autoing to 240p (when they normally auto to 720p) when nobody else is on the internet but me. I have reset the router twice now for 20 seconds each since it usually fixes the issue at least a little, but my download speeds are still averaging 2-5mbps. Usually, we have around 3 phones, a laptop and a ps5 on the internet which I know can be demanding at times but again, I went an entire month with regular speeds.. so, I'm unsure why the speeds would abruptly go south when nobody else is using the internet but me. Is there any way this can be fixed or do I just wait for it to fix itself?