You should never use pumped volume as an indicator of actual milk supply. Even in the best case scenario, pumping is estimated to get 60% of what the baby can. Besides...when did your milk come in? It is still in the normal timeline to be "arriving". I have birth on a Wednesday and mine was there in full force by Saturday morning--I definitely remember some pain during the first few days after.
Make sure you aren't dehydrated. It is VERY easy to get dehydrated after giving birth. Coffee wouldn't necessarily be the problem on its own...but if you drank a big one...and you were already a little dehydrated....then the caffeine could certainly exacerbate the situation. I was drinking nearly two gallons of water a day during the first weeks of nursing.
It probably isn't thrush this early on...not impossible, just not the most probable situation.
You could be experiencing some engorgement...are your breasts hard and much larger than normal? You can use warm compresses to help the milk let-down before you nurse (or pump).
Of course, if you're really worried called your midwife/OB...or find a local La Leche League group. The leaders are always full of information and support.