Being generally not turned on due to stress is so incredibly common. We all feel this from time to time. Desire also changes over time, and due to tons of other factors.
If you feel like there is something that isn’t right with your body, then by all means go see a doctor. You will know best if it feels like there is something wrong that shouldn’t be.
You can tell your boyfriend that it is perfectly natural for desire to be impacted by other factors. If its due to stress, it will pass as you relax. There will be times when you’re more into it, and times when you’re less into it. Tell him to hang in there, (and you hang in there too!) I promise it will get better!