Hi and welcome to the forum. To me the most overwhelming priotity is to get your pain under control and ibuprofen is excellent for muscle pain (assuming you have that in USA). I would suggest that you visit your GP initially and seek his/her advice and then see if you can get to see a physiotherapist.
Hope you get some answers and don't suffer in silence..it uses too much energy to fight pain when it can be controlled.
Cheers for now
Sarah's advice to start with your primary medical doctor is what I was thinking too. He can exam you, prescribe the best short-term pain relief for what he suspects is wrong, order tests and then refer you to a specialist if that becomes necessary.
Some type of physical medicine evaluation and/or therapy might be helpful too. That can be done by a physician specialist (a physiatrist - NOT psychiatrist!) or a physical/occupational therapist.
I'm sure you are worried because whatever is happening is traveling to multiple body parts. That's a good reason to get yourself checked out soon.
If you are worried about this being MS, what you describe doesn't sound anything like the way MS usually starts. But maybe you have MS and just now joined us to ask your question? And then maybe you didn't even realize your question landed here with us.
Whatever the case, I hope you find out what this is and feel better soon.
I'm not sure if you are diagnosed with a neurologic disease, so the following may or may not apply. Since MS is a disease of the central nervous system, it does not directly cause muscle pain. MS can cause neuropathic pain, or it can cause spasticity that can cause muscle pain.
Ibuprofen is an anti-inflammatory and while it may address the pain due to inflammation, it does nothing for the "cause" and like ALL NSAIDs, it may increase cardiac risks (like the COX-2 inhibitors.) All drugs have side effects.
When I hear "pain behind the knee," I begin to think "spasticity." There is no muscle behind the knee, but there are tendons that can be kept under tension due to spasticity.
You need to bring this up with you doctor (PCP or Neurologist.) A physiatrist may be helpful, but they tend towards the mechanical causes. If you are having spasticity due to a neurologic cause, they may not be the best choice. I didn't get much reduction in pain until they started an antispasmodic (Baclofen) plus a skeletal muscle relaxant (like Flexeril, Norfelx, Zanafelx) plus Valium at night.
The common warning applies: Just because I have MS, doesn't mean that every ache and pain is from the MS. I can still break a bone or twist an ankle or pull a muscle. Not every ache and pain is from MS.