Has your GP offered you a referral to a rheumatologist?

I'd want a second opinion.

And, to answer your question: Yes, OA can be symmetrical or affect both sides of the body.

Because OA, as with other forms of arthritis (or within the arthritis "family") can also relate to the automimmune system, coming down with something such as the flu could be totally coincidentally or a "trigger" - enough to push it to the point of having to notice it and seek med. attention.