Internal exams?

How often does your Dr actually do an internal? I had one early on and one last week when they did my strep b test. My Dr didn't say anything then about how low she was or whatever. I had a different Dr today (I have 2 that I regularly see) and asked him when they would start checking to see if I'm dilated etc and he said not until I get to week 39. I keep seeing people talking about how dilated and everything they are and don't know if my Dr doesn't check that until the end or if it's just because I'm so far at the end of the month lol