Mid-cycle bleeding on copper coil

[IToldYouIWasFreaky]

I posted this in the gynaecologist's AMA thread but the OP has left the thread so thought I would try here...

What can cause mid-cycle bleeding and is it a cause for concern?
I am 41 years old and have had the copper coil for about 20months. My periods were a bit irregular just after I got it fitted and I usually had some spotting in the couple of days leading up to my period. It's settled down now into a regular period, just a bit longer and heavier than pre-coil.
I am currently mid-cycle - due next period in about 10 days and I have been bleeding since Monday. Spotting at first but getting heavier over the past couple of days though not as heavy as an actual period. I do feel a bit periody too - achy belly and back and a general sense of blah!
I have made a doctor's appt but the earliest one with a female GP is not until 3 weeks away.
I know it's probably nothing to worry about but this is very unusual for me. I am usually so regular.
Might it be early signs of menopause?