Congratulations and welcome to the labouring (pun intended) club! May I ask how big is your baby now? Good to check with your gynae why you are having that much pain. While the back pain is normal, it usually happens more often during the 3rd trimester, especially nearing labour time. To ease your pain, one of the ways is to rest on multiple pillows. Get about 6 pilows and spread around the bed, 2 for your head, 2 next to your body, so there's a "hollow" for your back, and 2 for your legs.
Another method is use tennis balls to massage your back. Get your partner to put 2-3 tennis balls in a sock, and tie both ends. Get on kneeling position comfortably (on yoga mat or bed) with your arms supporting you on the floor . Then gently roll the sock on the back where it hurts. Do it a couple of times a day.
Hope this helps.