Hey, so. You're a healthy weight and you're eating enough. This might be tricky to get to the bottom of. But I'm just gonna ask some questions.   Have you been stressed out recently? According to the NHS website, stress could be a factor for missed/late periods.   Are you eating enough iron? If not, maybe introduce more red meat, leafy greens, nuts etc. in to your diet. Or if you're struggling to do that, maybe search for some multivitamins.   (Sorry for TMI) Are you on contraceptive pills? Again, the NHS website suggests that this might be a cause.   If this continues, I would suggest seeing your GP or your doctor. I'm not a medical professional here, but I just wanted to give input. I hope this helps! :)