Hello. Please tell me what to do: I'm 20 weeks pregnant and I've becom…

Hello. Please tell me what to do: I'm 20 weeks pregnant and I've become very nauseous and my stomach hurts a bit. I haven't overeaten or done anything like that, but I feel weak, I have no strength and I'm very nauseous. Until now I very rarely felt nausea and it was only a little. Right now I'm about to go crazy. Help me.