Very upset and unsettled baby..i need advice?

My 3 month old daughter has always been very loud..she cries all the time even though all her basic needs have been met.I have taken her to at least three different doctors who all tell me its in my head and their is nothing wrong with her. But i do not think it is normal for her to scream and cry as much as she does.. to me she sounds like she is pain her scream is blood curdling. I have done everything i can think of to try and help her. She has been diagnosed with reflux but that has been dealt with she is on medication and a thicker formula and it seems to have gotten alot better... but she is still crying..has anyone else been through this? did you find anything that helps. it is heartbreaking to see her upset all the time