Do you have swelling? Swelling will definitely cause issues, such as stiffness.

It's difficult to tell what may be going on with you. Is range affected? Strength? Weakness? Where in the tendon are you feeling pain, you say base, but not sure exactly where you are meaning.

Also, back of knee pain, could be due to a number of reasons, such as tight hamstrings or calves, also tight popliteus, issue with baker's cyst.

I've been working with a lot of soccer players lately getting ready for the season. You would do yourself good service by heading in to see a physio.

Sometimes issues such as laxity of ligaments in ankles and knees can be causing issues with ankles and knees. And please note, often ankle laxity causes knee issues, so it's not just ankle/ankle, knee/knee. Simple bracing can make a huge difference.