Here you have mention two issues that is back pain with thigh pain as well abdominal pain with cramping feeling in abdomen also associated with nausea. Usually this both will not be associated to each other. You can do treatment first which ever is disturbing you more. Check either the back pain started first or abdominal pain started first. If you use to have regular back pain problem then it will be related to either back muscle weakness or it can be related to spinal level issues like loss off curve, lumbar spondylitis, lumbar disc issues etc. How ever conformation can be done by specialist like orthopedic and physiotherapist with physical exanination and they may ask you to go for MRI of lumbosacral spine. And then based on report doctor will guide you treatment. If there is major problem at spinal level then it will be surgical correction and if there is mild to moderate issue it will be treated with physiotherapy exercises and treatment along with some medication as per your body need like calcium, vitamin d , muscle relaxants etc. You can also use hot pack for some more relief in pain. For your abdominal pain I suggest if it is first time it may be gastritis also so change your food habits. Do not take oily and spicy food. Maintain food timing. Keep water intake of 3-4 liter per day. And do walking regularly in night before you go to sleep. Have one anta acid pill daily morning with empty stomach for 15days and see how you feel. If it goes in 2 to 3 days well and good or else you need to visit a physician and may need to do ultrasound abdomen to rule out other possibility. Later can plan treatment as per the ultrasound report. Possibility are many with abdominal pain like gastritis, gastric ulcer, kidney stone since it is also associated with back pain, gallbladder stone, liver issues etc. How ever the conformation can be done only with ultrasound and proper physical examination only. Take care