Many women find it difficult to exercise their pelvic floor effectively on their own. Help is available through the NHS, in the form of a 3 month course of pelvic floor exercises under the supervision of a physiotherapist, who provides this information, guidance and motivation.
Your GP can refer you for this treatment, although many don't, despite PFMT being the NICE recommended treatment for stress incontinence (something to do with budgets!). Be prepared to fight your corner - we'd strongly advise you to persevere, though.
It may help you to get treatment if you can tell your GP that you have already tried self-help pelvic floor exercises. And you could even direct them to this site, if you want information to support your case!
If you can't get a referral, you can, of course, see a physio privately, if you can afford to.
You may also consider trying a device, such as the PelvicToner, which can help you do your exercise effectively. The PelvicToner is available on NHS prescription.
You can find a physio who can help you with your pelvic floor exercise on the Chartered Society of Physiotherapy website.