Really confused

Pradnya

I had my second <a href="https://glowing.com/glow-fertility-program">IUI</a> on 1 March. I had my periods on 15 March which were fairly light. After 10 days I had very little spotting for 3 consecutive days. We didn't try this month as we are stuck at different places due to lockdown. I have 28 days cycle and it's like clockwork but today I am 6 days late. What could be the reason??