Help! How to increase breast milk supply.

2 questions. My son is 4 months old. I have returned to work and my baby is in daycare. I take 4 to 5 bottles of breast milk 5 Oz each. But lately im not producing as much. I pump at work 3 times. I pump on my way to daycare and I breast feed him once he is home. Im on the verge of crying because I could barely make enough to supply his daily need at daycare. What suggestion or tips do you mommies have to boost supply.

I dont want to do formula, but let's say I had to replace at least one bottle with formula what are your suggestions? I want to do a gentle as possible transition so it dont upset his stomach or get him gassy, etc...