Husband low WBC count, vit d deficient, muscle pain, jerks going to sleep. Pcp, neurology, rhumatology, hematology. Nothing conclusive found. Frustrat?

D Walk yoga. Supplement his vitamin d and follow a healthy balanced diet. With lots of fruits and veggies, plenty of water and high quality protein daily. Walk two miles every day in that gorgeous san diego weather and find a yoga class to stretch those jerking muscles. Go slow and build up to this activity.
Well. Low WBC can be normal - but you can consult a second hematologist. As a second opinion. Vit d def is common -= get supplements. The muscle pain and jerking is possibly neurological - get a second neurology consult to confirm.
Micronutrients? Not much info to go on. You might try checking micro nutrients. This test is available from spectracell laboratory. Please supply current meds and past medical history to get a better response. Sorry I can't be of more help.