Sorry, Mel, I wouldn't be using infacol until about 6 weeks, but that's just me (and I'm not the one having to look after a screaming baby). Could you try gripe water first?
Also, I hear it can be really helpful to see an osteopath if you have an unsettled baby. We never went, but I wish we had've.
Maybe another trip to the dr might be helpful, as others have suggested?
Natalie used to cry a lot too. But she'd always settle down by 10pm. I really feel for you - I know how much pressure it can put on your family. Hope you find a solution soon.