No bijave, have never done six sectors in a B737...but have done six sectors in a TriStar in one day, many times, with long duty days, for five-six days in a row.
Tiring...well yes can be but consider---
If you don't, someone else will, like it or not.
Those are the realities...and are likely to remain so for a very long time.
Also, for airlines, paying overtime is always better for the bottom line than hiring additional aircrew. And, work crews to the maximum duty time...you bet. 'Tis called cost effective. However, if rostering is done correctly, a happy medium CAN be found for all.
Look at it another way...the airline that employes you is still in business, and supplying you a paycheck.
The alternative is the unemployment line. Take your choice.
Have CV's on my desk now, from VERY experienced guys, ready to work.
Suspect YOUR airline has the same.
And the guys represented in those CV's are after YOUR job.