Severe muscle pain at night 2 weeks post op breast augmentation. Is it normal?

This is not uncommon to have night pain and it can last up to 4 to 6 weeks.  I would still limit your activities and tapper off the narcotics if possible.  It can take awhile for the muscle to adapt and heal from your surgery but I think you will eventually be alright.

I would think that if it is muscular pain then the muscle relaxant would help more so taking your valium would be more useful.  Do you continue to have significant swelling on the left side only?

When you have heavy musculature the post op spasm and pain can last for a few weeks.  You may need muscle relaxers more than pain medication for relief.   Close followup with your surgeon.  Donald R. Nunn MDAtlanta Plastic Surgeon.