I am in a lot of pain. Sore and heavy breast unusual for me. Late period by about 4 days now. Spotted after four days only when I wiped with toilet paper so sorry if its tmi but it was only twice again unusual for me. Now still sore and tired. Feel like my period should start but its not. What should I do? What could it be? I never felt like this before

That is very common, sorry. Stress, poor diet, the hormone fluctuations we all go through, aging, and of course last but not least, pregnancy.
There might be rare conditions but doctors won't test for them until you have more symptoms and more time has gone by.
Soak in a warm tub, take Tylenol and ibuprofin, drink PLENTY of fluids, get enough iron in your diet (and avoid caffeine and fried foods and soft drinks), avoid constipation, and get enough rest. When lying down on your back, lift your pelvis up and hold, and repeat as many times as you can.
If this becomes a regular situation each month, your doctor will probably do an ultrasound and possibly suggest b.c. pills to even out your hormones.