What you describe sounds rather like my experience of dysthymia - a relatively mild level of depression that never quite goes away, although the more intense feelings might be more severe depression on top.

If it has a negative impact on your life, then that should be sufficient grounds to seek a medical opinion, if only for reassurance that you may not need meds. Dysthymia is tricky, because it's subtle and can be difficult to judge as anything beyond your normal.