Here are some other things you can try,
- Fill a water bottle with hot water, wrap it in a t-shirt and put that inside your sleeping bag.
- Don't drink warm tea before you go to bed, as
Don't drink warm tea before you go to bed, as that will increase the chances of having to get out of bed or being uncomfortable all night long.
When your bladder is full, your body is expending energy keeping that liquid warm. If you empty it out, your body needs to expend a little less energy to stay warm.
On the other hand, eating before bed will give your body fuel during the night.
Make certain that your sleeping bag fits you properly, as if it is too long there can be an empty space down by your feet that will hurt your ability to stay warm.
Consider getting a warmer sleeping bag.