Sorry to hear the negative result. Pressure affects your hormone and delay your cycles. If you worry, ask for blood test on day2 and 21, some Chinese Dr. asked about that so they know what need to be improved. Try not too worry too much. Many of us here has similar experience. "Add oil"
It is quite unusual that your M period is ever longer and longer, I think your Chinese doctor is no good (同你唔夾). Suggest you to stop seeing Chinese doctor and go to see 西醫 to check hormones: FSH, LH, PRL (Day2抽血驗) and 黃體酮 (Day21).