This pain you are having seems quite severe, and it is clearly limiting your activity if it comes on with as little as 30 feet of walking. For this reason, you should see your primary care doctor
for an evaluation. There are many different causes of knee pain, but your doctor will be able to help point you in the right direction.
For example, if you are physically active with a lot of higher impact sports, such as running, then an overuse injury, such as runner's knee, will be high on the list.
Similarly, if you have a history of a severe knee injury in the past, then a torn ligament or damaged cartilage will be higher on the list.
Finally, if you are middle aged or older (it is not clear from your question what your age is), then wear and tear arthritis
might be more likely.
Your doctor will perform a careful examination of your knee. Based on what they find, together with what they discover in your history, they may want additional testing, such as x-rays or an MRI
of the knee. They will also be able to recommend the appropriate next steps either in treatment or in referral to a specialist. Make an appointment with your primary care doctor today.