Is there really only a 6 month window in order to lose all of pregnancy weight or you will most likely carry around an extra 20 pounds 10 years later?

i find it really hard to believe that there's only 6 months in order for women to get back into their slim figures after the baby comes due to the fact that a baby is a new, stressful, needy, dependant on others being!
i barely had time to pee when my son first arrived because of how dependant, difficult and time consuming everything was[and still is!]
I started going to the gym with my sister inlaw when my son was 3 months but again, it was an on and off schedule because some nights my son would be up all night and i would be way too tired to run to the gym!
now my son is 7 months, and i am going to the gym more often than before which is good, but i still am stuck at a platue in my weight loss..the pounds will not budge know matter what i do.
its frustrating and then feels kind of depressing after just reading that theres only a 6 month window to lose weight after baby..

and advice or comments?