Oh, I can't take it anymore...

We have added solids for 3 days now. I don't know whether it is because of constipation or not, she has been sleeping really poorly these three days. I am so frustrated and desperate, and I almost want to try controlled crying. Please help me hang in there.
Doctor has checked her and she is not ill. But For no apparent reasons (other than OT and constipation), she just can't settle even at bedtime and before naps. For the last two days, she has been crying on and off for almost an hour before naps, and it happened again at bedtime tonight after grunting for 20 min, and then I went in as she became louder. But every time things becomes a mess after I went in.
Last night, she cried from 11pm-2am. 3 long hours. OMG, this is totally crazy. I fed her at 12am, but she still cried and wouldn't settle, and finally I fed her again at 2am, and she fell asleep.
I really don't know whether I should continue with PUPD, or maybe just give up, just rock her or whatever works. She just starts to cry really loud once I say I will put you down. And then I pick her up again, hold for a long time to calm her down, and try PD again, and she cries again, this just repeats itself... 3 hours is too long. She cried louder and louder and it became more difficult to sooth her.
And what's worse, I don't know where is the end. Every time it looks like things are getting better. Then suddenly it gets worse.
Tracy said: Start as you mean to go on. I really don't know how to go on. I don't want to give up because I know it means more crying in the future. But what should I do if she just cried and cried? I called my mom to come and help me and finally she rocked her to sleep tonight.
Because I can't help her fall asleep, I am frustrated, desperate and also angry. I don't know what to do. I cried and cried, and it is so hard to deal with my own postpartum depression and her crying at the same time.
Please help me...