After three weeks, the fact that she cries at the same time every day is pretty telling, but there are a couple of things I'd like to ask you before I say "yeah, it's colic" - when she cries, is her belly hard or bloated? And does she have trouble pooping, or does it come out easily?
I'm asking because real colic has this super regular pattern (what you're describing is classic), but evening crying in small newborns can also come from reflux or other stuff, especially if her belly isn't tense. The pediatrician should rule out milk allergy - whether it's breast milk or formula - before assuming it's colic, because if it were that, nothing would change by massaging or trying different positions.
If the pediatrician has already ruled out other causes and the situation is exactly what you're describing - same time every day, desperate crying, nothing calms her for hours - then unfortunately yeah, it could be colic and in that case the most realistic thing is it'll pass on its own in a few weeks, two at most. In the meantime you can try her on her belly, rhythmic movements, maybe one of you holding her during that time so the other can rest a bit.