بسم الله الرحمن الرحيم
According to Hanafi Fiqh, crab is unlawful, so it is mandatory to avoid drinking its soup. There is difference of opinion about prawn. However, it is better to avoid eating prawn and drinking its soup. Consult any hakim or doctor for the treatment of your disease. If halal and lawful medicine is available to cure the said problem then you should not use the said soups.
Allah knows Best!
Darul Uloom Deoband
This answer was collected from the official ifta website of Darul Uloom Deoband in India.