Extreme weakness at 31 weeks pregnant

Almost every single day I feel super weak in my arms and my legs like super bad and just feel really sick! I can go outside for like 5minutes come back in and I'm in so much pain it's ridiculous sometimes I wanna go to the er but my boyfriend just says it's cause I don't drink a lot of water which I try too. But this is an every single day thing that sometimes it even hurts to text like right now my left arm is hurting bad what could this be? Should I go in tomorrow if I wake up like this and tell them it's an every day thing that I feel this weakness?? Sometimes I just lay on my bed and I can't even move 😔