Lower back pain very common its just another thing that people with crohns sometimes have to put up with. Testing may find no answers, just like it can be hard for some people to get a crohn's Dx. Try not to over worry, have Xray to get it checked out have a bone density test to check for osteo. Your bloods will let your doc know if it maybe comming from a deficency. I have had crohns for 30+ years and have back problems. Ask yourself is it intermittent pain some days not others. I don't know how long you have had crohn's for but you may find you will get other intermittent pain with other parts of your body like legs, arms, muscle and joints. They can be signs of a flare up at times. Just because you don't have bowel symptoms at times this horrible disease can still be attacking other parts of your body. All Crohn's people are different. If you get any acid relux heart burn please get it checked outas I thought I was just getting mild heartburn till recently when I had a attack which I thought was a heart attackand now I can add COPD to my list as the stomach acids can get into your airways.
by the way you do not seem over dramatic i also almost lost my life at the age of 22 from crohn's complications had surgery to remove mass the size of a softball cause by crohn's had part of ileum and cecum removed resection and had tpn line put in then became septic was in icu for almost a month dr told my family to say there goodbyes came back from it now 30 but every time i get a flare witch is often i get scarded it will end up bad
i have crohn's and do have lower back pain i have come to learn this is a common problem with people that have crohn's so did some researched talked to GI and this is what i have learned it could be(1)osteoporosis ,due to poor nutrients absorption calcium deficiency (2)muscle tension, due to bowel inflammation (3) sacroiliitis ,due to inflammation of the sacroiliac joint (4) or inflammation of other joints in back.Depending what it is is how to treat it with meds massage hot bath psychical therapy ask the Dr he can help