In so much pain

My lower stomach (below my belly button) has been hurting so bad since yesterday...my back has been hurting as well to the point where it’s hard for me to walk and lay down. I thought it was early labor (im 30 weeks 1 day) but the pain isn’t coming and going it’s been consistent since yesterday afternoon. I went to the doctor this morning and my cervix is closed and she said I’m cramping because of my lack of food intake. Which is weird because I’ve been eating so much lately. So now I’m thinking I could be constipated that’s why I’m in so much pain but I need some other opinions.