Yes, you should contact a doctor
, and yes, it could be a part of giving birth. Natural births and births involving the use of an epidural should not have any difference when it comes to your post partum symptoms. The epidural is valuable for reducing pain during childbirth, but it does not affect the pelvic musculature in any way, except for some suggestion that there might be less tearing of the pelvic muscles in the absence of an epidural.
Given the fact that you are continuing to have symptoms even 6 months after the fact, you should discuss your concerns with your OB/GYN or midwife. You will likely need to have a physical exam, and will be asked some further questions about your urinary continence as well. It is notable that multi-parous women (women who have had more than one baby) are more likely to have problems with the musculature of their pelvis.
In other words, it could be that the repeated trauma to the pelvic floor is to blame, rather than anything specific that occurred during this most recent birth. Again, the only way to know and to address your concerns fully is to discuss them frankly with your OB/GYN or midwife, as these symptoms are not a normal part of a natural labor.