Why is my baby crying nonstop?

Why does my baby keep crying nonstop?

So my 3 week old has started crying all of the time for the past 5 ish days. She’s only ever not crying when she’s sleeping, eating or bouncing in the air upright. She’s EBF directly on the breast and we have suspected I have a fast milk flow. I’ve tried burping her more, feeding reclined in a football hold, and scissor clamping my breast lightly with my fingers. She still has loud audible gulps when eating and drinks milk fast and sometimes clicks, pulls off breast a bit to make a more shallow latch, or coughs. She only drinks from one breast every feeding because I think she’s getting a lot from just one. She’ll eventually fall asleep on my breast and not take the other because she’s asleep. But the second I start burping her or put her flat on her back in her bassinet she starts getting very fussy. She only wants to fall asleep on my chest. When she cries she arches her back, stiffens up her whole body and flails her arms in the air. She burps but it’s hard to burp her because she’s crying like that. We try everything to figure out what she wants including putting the Frida windi up her to get gas out, which works but she’s still a bit fussy after. She also hiccups often and has spit ups with the burps and in her bassinet on her backs. Lastly, she has been grunting and wiggling in her sleep a lot lately which I’m not sure what that means. Please help because her crying is just so often I suspect she might be in pain maybe and I hate to see her constantly upset and never have a break from crying. Thank you.