Back pain and sciatica are more common in pregnancy because of the action of the pregnancy hormones which cause softening of ligaments, predisposing to injury. The weight of the growing baby and uterus also has an effect. Unfortunately, the pain of sciatica can be difficult to alleviate with painkillers. I would recommend that you arrange to see a physiotherapist who is experienced in treating pregnant women. You will be assessed and they will be able to give you appropriate exercises to do to try to strengthen your back and improve your posture. Swimming (as long as you don’t swim breaststroke with your head out of the water) is also likely to be helpful. If you do wish to try some stronger painkillers I suggest that you try a codeine and paracetamol combination, such as co-codamol. Codeine is what is known as an opioid analgesic (related to morphine). The risks associated with the use of codeine apply mainly to the last three months of pregnancy. It is very unlikely to have harmful effects when used during the middle months of pregnancy. It may however cause constipation or nausea and it would be wise to use it as little as possible.