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People respond differently to exercises; if you can detect no improvement at all, then you need a different type of exercise. Pelvic floor exercises are often taught as a single 'catch-all' technique; a bit like saying that pressups are the only gymwork you need to do. Your genital area has many different muscular functions going on; each needs a different type of exercise to maintain and improve its ability.
(There are also a lot of different responses to surgery, so the horror stories and the happy endings are equally unlikely to apply in your own case.)
Hysterectomy will have been recommended if the problem seems like a 'prolapse' (latin for 'falling down'), rather than just weakness in your pelvic floor. (You may have the beginnings of one, rather than the full effect. A surgeon would probably see progress towards a full prolapse as inevitable.)When you're giving birth, the effects on your birth canal are highly individual; so is your recovery from a 'tear' or a deliberate cut (episiotomy). There are some circumstances where the muscles 'down there' are so badly damaged that surgery is the only answer, but these are very rare.
Most doctors are aware of 'pelvic floor exercises', but are ignorant of the range of different exercises, and their specific effects, that can be used for pelvic (not just pelvic floor) muscular rehabilitation. In academic studies, the results are mixed, because differences betwen effective and ineffective methods are not generally understood.
URINARY CONTINENCE isn't just down to your pelvic floor; you can improve control by trying to stop and start your flow while peeing (it might take a while before you can stop in 'midstream' at all; keep trying anyway, and you will eventually find the technique). As you practice, you will feel a difference between this and other pelvic floor exercises. Try peeing different musical srhythms, or mesages in morse code.
When exercising for GRIP, you need to work on your 'hold'. Just 'twitching' your pelvic floor isn't going to enhance your grip, regardless of how hard you do it, or how often. Start by trying to 'hold' for a count of three. Work upwards, by threes if you can, until you can comfortably hold the grip for fifteen seconds. You should start to notice an improvement by then.
( EDIT - Some Physios also teach a '4-stage grip', where you learn to grip gently, more firmly, very firmly, and really hard. This 'ladder' is repeated every time you practice.)
VAGINAL MUSCLE TONE (airspace, sensation) needs a different type of exercise. The entire vaginal wall is lined with muscle, and just like a leg or arm muscle, this can be damaged by extreme stretching. it can recover, though, and you can stimulate this with the right rehabilitation exercises. Specialised weights are available for pelvic floor exercises. These initially activate only the pelvic floor (basically, you keep them from falling out by tensing up the muscles) but as your familiarity with the technique improves, you can lift them further inside by activating different muscles.
EDIT: The best technique for these is to try for a 'bouncing' action, so you're squeezing it hard and rhythmically, not just 'keeping it in'; this allows you to 'tune in' to the progress you're making, and to judge whether you're in the mood for a hard progress .session or some determined maintenance.
If you can't get the specialised weights, a short fat carrot (well scrubbed) can substitute. Inserted blunt-end first, you can exercise while walking about, by trying to keep it in against gravity. Lying down, you can try to push it out as you insert the pointy end.
All of these are very slow processes; the longer you have left the problem to develop (or pursued an ineffective remedy), the longer it will take to resolve. However, you should start to see some improvement quite soon, once you find the right technique.
There is also a traditional yoga technique, called the 'rising (or 'lifting') lock' (or sometimes 'the great leap'), which helps to support the internal organs, and practiced regularly, this can relieve the pressure contributing to a prolapse.
EDIT: Some Pilates teachers specialise in this kind of physiology; you'll need to ask around for a class that's popular with new mums. There are specialised physiotherapists (pelvic rehabilitation) and clinics. You can be referred by your GP. The yoga thing is best taught in person by a traditional yoga teacher. You can find one of these through the 'Wheel of Yoga' organisation.