I have a constant pain in my lower right side of my back. what could this be it just started today?

Hard to know: Low back pain is very common and is typically due to muscle strain. Typically rest and over the counter pain medications are a good first step. If the pain worsens or doesn't resolve on its own, or if you develop other symptoms like leg weakness or abdominal pain, you should call your doctor.

Lower back pain: Being 30yo i doubt you have had a back problem before so a kidney stone could be but this usually comes on quickly and usually alot of pain. You could have picked up something heavy and have a muscle strain to your muscles this causes pain on movement and feels better at rest. Take 800mg of Motrin or see your doctor if severe pain.