How old are you @lockdownmadness?
If you are in the peri range - normal ranges- so anything from mid 40s upwards, it's normal peri. I don't think you need to see or talk to your GP just yet.
Everything you describe points to peri. The sore boobs- cycles change and there is less progesterone which results in sore boobs sometimes. PMS can get worse or appear for the first time as we approach menopause. A short cycle- like 2 weeks early- is normal. Mine dropped from my usual 30+ days to 17 days a couple of times.
The mood swings and brain fog you describe are again, typical of peri.
Irregular bleeding is an issue with women post menopause when they have not had periods for a year or more,
For anyone whose cycles go haywire, in peri, it's absolutely normal.
It's not a reason to contact your GP. You don't need an internal exam, or a scan at this stage. What they would tell you is to keep track of your cycles for 6 months and see the pattern.
Have a read of the info on the website of Dr Louise Newson (it's called My Menopause Dr) and is really helpful.