Internal server error

For the last two months, I’ve not been able to update posts manually as I keep getting an inter an internal server error. It used to be 404 but I’ve also seen 500 and lately there’s no number to it. I don’t know what could be causing it as I haven’t recently installed any new plugins. It’s very inconvenient and is really slowing me down. It means I’m losing any updates I make to any posts. Refreshing over and over makes no difference.
Any ideas would be appreciated