Exercise will F up your system - Depending on the type of exercise and depending on you. By intense, you mean intense aerobic or intense strength based, like weight lifting? Expect a lot of variability associated with exercise after the honeymoon. But, of course, that doesn’t mean you should do it, just that you should be aware of its effect.
6 hours might be long enough to to deplete your liver of glucagon (sugar it releases) and produce severe lows many hours later (perhaps a day later, or 2 days later).
Answer: Yes, its supposed to be like that. I would not call your data “unpredictable.” After honeymooning ends, it will become more “unpredictable.” The younger you are, the more “unpredictable,” it is likely to be. Females, generally have more variability than males. As you age, you might expect variability to decrease. Technological tools sometimes help decrease variability (but, sometimes they make it worse).
Some people have additional conditions that make for high unpredictability, like gasteoparesis. Or, see the addison’s disease post. Managing Type-1b Diabetes with Addison's - #17 by JDavid