This is so difficult. I agree that you should not delay in getting help, and in principle go to your GP. This will not be the worst they have seen!
However, in these strange times, with long waiting lists, I am going to suggest a slightly different route, if you can afford it. Use the Society of Chartered Physiotherapists to find one specialising in pelvic floor / gynae:
www.csp.org.uk/public-patient/find-physiotherapist/physio2u
She will assess you, and on that basis, may suggest some exercises if appropriate. She will do a referral to your GP explaining the problem, and if you need to see a gynaecologist, the referral may be done more easily.
I would also consider getting an appointment with your practice nurse, who could talk with the doctor, and give you some specific advice about constipation. You may think that after a lifetime, you are used to managing it, but this is a slightly different situation.
However you handle it, please don't wait. I bless my mother who taught me that my health was more important than temporary embarrassment. Good luck