Welcome to the forum.
If this took place only after you son's birth there are two possible explanations that I can think of.
a. Your hormonal levels have changed.
Go to the hormone restoration website for details. It's far too complex to explain it here to you.
Just take your time to absorb the information at your own pace.
Also Dr Lam's website has a good tutorial on adrenal fatigue and hormones.
b. Your delivery had a possible traumatic effect which acted as an activator for the onset of an inflammatory condition like arthritis.
Let me know if you need any further details or suggestions.
You may pm directly if you prefer.
Best wishes!
Niko
What leads you to believe you have elevated inflamation?