Two cycles in one month, with this one heavy and clotted, usually means you didn't ovulate properly that month.
Thyroid changes, stress and fibroids can all cause this kind of hormonal swing. Needing a pad change every 2 hours with clots is heavy enough to need a proper look, not just waiting it out.
Next Steps
A pelvic ultrasound and blood tests for haemoglobin and
thyroid usually explain this. If pregnancy is possible, take a urine test first, since heavy bleeding needs different handling then. Please see a gynaecologist this week, sooner if the heavy flow continues.
Health Tips
Go in urgently if you feel dizzy, your heart races, or you're soaking a pad within an hour.