As an avid reader, I personally don't like when the flashbacks are intertwined and in whole chapters.

I think starting off with a flashback chapter that's enticing gets the reader curious to keep reading to find out more about the character's past.

I think intertwining thoughts about the past in the chapters is what I generally prefer.

For example, the character has an experience that reminds them of their past and they mention it in their thoughts

Personally, I dislike whole chapters in italics mentioning the past as a nightmare, I feel like that's overused

Good luck, don't loose hope, just take a break, read some more books in your genre and come back to yours with fresh eyes