A well known cause of pain,in the case of common back pain especially waist pain & neck pain resulting from physical exhaustion is marathon sex,which while in it involves excessive spine movement.For those not used to such rigorous exercises could as well lead to pain after wearing out of the euphoric pleasure of the encounter.Sex is like any other physical exercise,a wrong approach to it could lead to agonizing pain in the back(especially the waist)and it's believed to be one of major sources of contracting waist pain.On the other hand,if you have existing pain in the back,it will surely impact on your relationship.This is a problem people dont discuss,the reason for this attitude is that people who are suffering it feel that they may be the only ones having this problem and therefore are embarrassed to talk about,even with a physician or therapist.Be careful how you use your back during sexual encounter.The back is a big and compact organ having nerves,blood vessels,ligaments,muscles protecting the delicate spinal column that houses the spinal cord.Any serious injury to the back structures can cause unimaginable consequences,not only to the immediate structures of the back but also to other vital organs in the body.Vital organs such as the erectile structures in the private part can be rendered terribly ineffective and will be in a sorry state of inactivity because of disabling back pain! So my advice to you is,if you are experiencing any of the above and are not able to resolve them with your partner,discuss it with your physician or seek help from a psychiatrist or psychologist.Most problems are successfully and rapidly resolved.