Hello,
The cause of irregular periods could be due to hormonal imbalance, stress, chronic illness, polycystic ovarian disease, thyroid gland disorders or diseases, pituitary gland tumors or cyst, galactorrhea, prolactinomas etc. You should consult a gynecologist and get examined and investigated as soon as possible to know the exact cause of all these episodes.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing
Many things can delay a period so it could be nothing. But protection isn't 100% effective so since you're late I would take a pregnancy test just to be on the safe side and rule it out because it is still possible.
Stress, hormone imbalance, SDT, illness, etc can all delay a period.