There's a term for this called postpartum joint pain. Your endocrine (hormonal) system undergoes large shifts when you give birth and its possible that some of your pain could be related to that. One hormone called relaxin actually causes your joints to loosen up and the withdrawal of relaxin after birth and your joints trying to return to their normal state can cause pain.

Postparteum joint pain is not that unusual and usually does disppear over time but be sure to tall your doctor what you're going through as only she/he can give you an accurate diagnosis.

If the pain does not disappear you might want to check out other options such as fibromyalgia but for the great majority of women the pain disappears as their body readjusts to its new status.