Late period 3 years after tubal

3 years ago I had a tubal after having my last baby via c section. My cycles are usually on time every month. If the app says it’s this day, then it is almost always that day or a day or two before or after. This month I’m currently on day 35 of my normally would be 28-30 day. Most months before my cycle starts 2-3 days before I have night sweats and other symptoms. However, I have no symptoms or feel like it’s coming. I did take 2 test a few days ago which were negative. At what point should I be concerned?