I have constant flank back pain which started 1hr ago. sometimes there's sharp pain in left back/abdomen when i move a certain way. worse when laying.

Strain vs Stone: Two most likely causes are a low back strain or a kidney stone (nephrolithiasis). Kidney stones usually cause a pulsating pain, radiating to groin with no position that relieves pain, may cause blood n urine. Back stain will cause worsening pain with certain positions/movements depending on location. Try ibuprofen and moist heat. See Dr asap if increased pain or persistent symptoms.