Three months without a period, after a run of lighter cycles before that, usually points to a hormonal shift rather than anything structural. You haven't started again even after the spotting in September, which fits that pattern. Common causes at your age include
thyroid imbalance, a raised
prolactin level, stress, a change in weight, or early PCOS, though no acne or facial hair makes PCOS a bit less likely, not impossible.
Next Steps
A blood test covering
thyroid,
prolactin and your reproductive hormones, together with a pelvic ultrasound, usually finds the cause. Mention the September spotting and your homeopathy course too, since the timing may be relevant.
Health Tips
If your period doesn't return on its own soon, please see a gynaecologist for proper testing rather than waiting it out further.