I have had back of knee pain for a few weeks, sore when straightening from acute angle and hurts most if a twist happens. Should I use a support?

Investigate why? Sounds like it could be a Bakers cyst! These are knee fluid collection in a cyst behind the knee, likely as a result of trauma, wear and tear,i.e. A torn meniscus?, should get an MRI to better understand why this is occurring!A support may make it worse! Need to find out what causes the fluid buildup up! May need to aspirated knee, please see a rheumatologist or Ortho, Best!