New to Minecraft

So I’ve played Minecraft before so I get the whole idea. But I just bought it on ps4 and I’m hooked again. I’m playing survival mode on hard and it’s super fine and very different from Minecraft servers.

But there are some strange things, like for example why does my health bar keep going down when I try and move? My food bar is full so it can’t be because of starvation.

I already died and lost my original map, so I made a new map. The whole thing seems to be filled out already, even though I haven’t traveled that much farther than my starter base. Also there doesn’t seem to be any direction on it either for some reason. Do I really need a compass?