I don't know whether this will give you hope but here's something I learnt shortly after my son's birth.
I visited a friend of mine in Belgium, who is a physio and was going through specialist training in post-birth care.
When I described the way pelvic floor exercises are recommended in Britain she was HORRIFIED.
Apparently, doing many fast repetitions actually relaxes the muscles in the long term.
Instead, you are meant to do very few, very slowly, and stop for at least 10 seconds after each.
So - sorry, this is actually quite difficult to describe in writing - the idea is: contract gradually and hold for about 15 to 20 seconds (it's very long) and then relax gradually. Stop for 10 seconds and repeat.
Better to do 5 well than 10 or 20 in a rush.
In France and Belgium all my post-baby friends have been prescribed (on the equivalent of the NHS of course, argh!) ten sessions of what they call 'gymnastique hypopresssive' after birth and it's totally amazing. Pilates (by a decent teacher) is the closest you'll find in the UK.
But in short, GO SLOW to build muscle strength, rather than relaxation.
Hope it makes sense!