hi loomoo
Firslty welcom to the forum
If you are injecting 4x daily, I assume that you are on the basal/bolus regime...
You still take your background insulin the same as usaual, with the quick acting insulin you need to inject when you eat durning the night, it is hand if you have a idea of the ratio of insulin to carbs you need for your meals, but you might find that this is different at night than durning the day...
So test more frequently until you are sure that you have the right ratios, when you are asleep after the shift, if your basal insulin is correct this should't cause any problems...
If you on starting a new run of nights, inject our insulin as usual durning the day, but remeber that you will have to have extra injection to cover any food that you eat..