Im having serve back pains, please help?

well im 27 weeks pregnant and i have been having the worse back pains imaginable. i think it could be a trap nerve or something but im not completely sure. i cant walk anywhere because it just makes it worse, i cant sit down for the full dinner. the only time im not in pain is when im lying on my left side as the pain only seems to be on my right side so it must just been taking the weight of my right side. sometimes the pain is so intense that tears will be streaming down my face and i cant move or breathe correctly. ive spoken to my midwife about it and she said she would refer me to a physio but that was 5 weeks ago and i havent heard anything and its gradually getting worse, i went and seen her on tuesday and she said she would chase it up but i just want any advise on what it might be and i could help it at all? ive still got 12 weeks or so to go and i dont want to be in this much pain for that length of time. thanks for any advise given