EMB ERJ 145 ER/LR
Confusion
ATC Issue All Types; Aircraft Equipment Problem Critical; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance
Air Traffic Control Issued New Clearance; Flight Crew Became Reoriented; Flight Crew Returned To Clearance
Procedure; Weather; Human Factors
On taxi; issued return to clearance frequency for new route. New route entered in FMS. Issued a 1 hour wheels up time and a place to hold. While waiting; Dispatch sent another route. 3rd route entered and cleared with clearance and ground. Ground issued taxi instructions and Tower. Flight departed. On departure ATC assigned fix not on 3rd flight plan...fix from 2nd route. ATC confusion and told to slow while looked for correct flight plan. Captain copied and re entered 2nd flight route from ATC; First Officer flying.  First Officer tried to check route in FMS but was distracted by flying duties and unable to verify FMS before ATC queried if on a heading. ATC issued vector back to route. Captain missed entering an airway between fixes and ac departed planned course. Multiple routes; should have verified first fix/route with Tower; should have used automation more to allow for better FMS change verification.
EMB-145 First Officer reports being cleared via three different routes by ATC while awaiting a wheels up time. Once cleared for takeoff the crew is cleared direct to a fix on the second route. After some discussion with ATC the second route re entered in the FMC; but an error is made causing a track deviation later in the flight.