Hi. i have been have neck pains, and pains mostly from the shoulders up, but also in the lower back. could it be an infection or just a sprain?

Neither likely: Almost certainly not infection. Sprain is injury to ligaments..Also unlikely. More likely is strain of back and or shoulder and neck. Check if you are doing inappropriate exercises or overly stressful activities at work. If there is no neurological involvement (numbness, shooting pains, weakness, electric like shocks) this is likely muscular. If not improving with rest, NSAID see your pcp.