I would make sure you are drinking LOTS of water, next to nursing on demand, it is the best way to keep supply up. Additionally, you can take Fenugreek capsules up to 3x a day, which increase milk in many moms, also coconut milk and Red Raspberry Leaf tea works well for many. It is likely that you just experienced the typical evening depletion...it happens with most moms. The heaviest supply is first thing in the am and mid am, then in the evening the suply is usually lower and slowly comes back up as approaching morning. Keep nursing on demand whenever your baby begins to show signs of being hungry. Keep up the good work and don't worry! If you are health conscious, you know that you are giving your new baby the very best thing that they can get...Mommy Milk! Way to go and keep it up! I recommend joining and online nursing support egroup (they are soooo valuable in your long term success!) and possibly attending support groups such as the one help at Morton Plant in Clearwater or even a Le Leche League meeting. Yo get lots of great advice and answers and support from other like-minded moms (most Dr's, unless they are very nursing-friendly don't give very good nursing advice, after all it's the formula companies that give them $!)
Best Wishes!