I can almost guarantee there's an underlying cause, but I am far from knowledgeable enough to know what it is.
Regardless, one thing I'd recommend it trying to get extra sleep. I'm sure that it's tough with a newborn but it really is amazing how much being behind on sleep can affect your body systems. Also, sleep is necessary for your body to recover from a hard day of work, stress, toxins, injuries, etc. Whatever it is, sleep could only help. I recently got over a minor stomach bug and had similar symptoms for several days afterward. Finally, my husband sent me to bed after church last week (even though I didn't think I would be able to sleep) while he played outside with our three little ones. Four hours later I woke up and have been feeling fine since, with the exception of mild lingering morning sickness!