Hi abellababy
The pain is caused by all your joints loosening in preparation for labour. For some women the pain can be almost as bad as a broken bone and is due to the ends of the joint in your pubic bone rubbing against each other. Try moving slowly and keeping your knees together. If it is unbearable you can try taking panadol or panadeine.
An increase in discharge is common late in pregnancy. If it is thicker than water then it is just your cervical mucous, if it like water then you should get it checked.