How often should we have smear tests?

Hello all,

Just wondering how often we should actually have smear tests? I only ask as I wonder if I am due one. A bit of history, had a few abnormal smears from the age 17 to 23 which kept needing repeated but last one at 23 was fine. So a few weeks after I got the Mirena coil put in(4 years ago) my cycles have always been 5-6 weeks apart even with the Mirena coil so really surprised when now my last 3 cycles have only been 2 weeks apart each, much heavier and longer than I am used too. I am experiencing period like cramps almost daily and have bled after intercourse a few times, also experiencing an increased amount of discharge sometimes with bits of blood in it. The last few times I have had intercourse I have been doubled over with pelvic pain for about an hour or two afterwards. I have an appointment at doctor coming up but my friend asked when my last smear test was, which was when I was 23, I am now 27 so should it be 3 years from I was 23 or 3 years from the 25 year old starting age?
Thank you in advance for your replies