My question is what causes these little blisters that keep popping up on my fingers?

Probably pompholyx. This sounds like pompholyx ( dyshidrotic eczema ), although fungal infection or other conditions may also be the cause. Recommend you see a physician or dermatologist for definitive diagnosis and treatment. Look up "pompholyx" on the web, or try this: http://www.patient.co.uk/health/pompholyx-leaflet.