There is not much reason to worry at this moment. The information provided by you is not sufficient to provide a good opinion. If someone comes to me with lump between hip and spine and radiating pain, I would ask them these details to zero-in on my opinion: When did you notice the lump first? How is it progressing since then? do you feel radiating pain during walking or sitting also? do you feel numbness and altered sensations over the leg and foot? is there local increase in temperature over the lump? by getting answers of these question, i can give opinion regarding origin of swelling whether it originated from muscle or from nerve and suggest further investigation such as MRI if nerve origin and ultrasonography if muscle origin. I would like these details from you to help you further. Hope this answers your question. If you have additional questions or follow up questions then please do not hesitate in writing to us. I will be happy to answer your questions.