With a few exceptions, every employee's contract is entirely separate to that of any other employee. For example there are offices in the City of London where two employees,sitting side by side and doing exactly the same job, might have vastly different contracts. Fred might be getting £20,000 p.a. with 28 days holiday and no 'perks'. Joe, on the next desk, could be getting £100,000 p.a. with 40 days holiday and loads of perks. That's perfectly legal and by no means uncommon.
So generally you've no right to expect to get what anyone (or everyone) else gets. The only exceptions are when different pay rates between different groups of workers result in unlawful discrimination (such as on the grounds of gender or because one group of employees are part-timers whereas the others are full-timer employees) or when there are standard pay scales agreed through collective bargaining or set by law.
There is no statutory right to a higher rate of pay for overtime or for working unsocial hours. (In some jobs, such as junior hospital doctors, the overtime rate is far lower than the normal pay rate).
So, unless you can show that unlawful discrimination is taking place, I can see no valid argument for getting a pay rise.
There's nothing illegal about working 7 days in a row. When I worked on the railways I was involved in setting up a new shift system. That resulted in a working 'block' consisting of 7 weeks, with several continuous stretches of 10 or 11 days work within it. (My colleagues unanimously voted in favour of that pattern of work because it also meant that we got several periods of up to 5 successive rest days within each 7 week block).
Chris