Overactive letdown advice needed

After a rough start to breastfeeding with a bad latch, things started to finally feel doable (but still really tough)after 3 weeks post partum. Now my baby and I are struggling with overactive letdown and we are both in tears. Many times, She acts like she's starving but is afraid to latch on to my breast due to the strong flow .it breaks my heart to watch her acting so hungry but denying herself to eat. Also, she is experiencing painful gas, gagging, choking at the breast etc. she has been crying in pain so much the last few days. My flow has been really strong since a few days after her birth so I don't understand why she's suddenly being affected by it. It breaks my heart when she will only feed for a few mins, cry and scream at the breast, and the eventually give up.  I'm so tempted to just throw in the towel and switch to formula. I'm definitely not opposed to formula but after making it 3 weeks of breastfeeding, it makes me sad to think of denying her that bond. At the advice of an lc, we started block feeding yesterday, no results as of yet. Any advice other than to use my pump would be greatly appreciated.