Menstrual like cramps with back ache

Has anyone else been having menstrual like cramps with some back ache? I'm 25 weeks. I been having this constant strong cramping since yesterday evening. I tried a warm bath/shower, drinking lots of water & laying down on my left side, but when I lay down the cramping gets more intense. Earlier today I was having contractions close together when I walked almost 2 miles. I called my doctors office but haven't heard back from the on call doctor. I'm debating on if I should just go to the ER?

UPDATE: I did go to the OB ER Triage & was having contractions. My cervix is still closed which is great, no uti & I wasn't dehydrated. I have an infection called bacterial vaginosis. Which was causing the contractions. They we're getting stronger & closer together so they gave me a shot to stop them. I have still been getting them again but the er said if they get worse to go back. I have to take the medicine for 5 days & after hopefully they'll stop. Thank you all for the warm thoughts & advising me to go in.