Waking up in the middle of sleep is a common form of insomnia. Insomnia is not a disease, it is a disorder, and a disorder might have a much wider range of causes than a disease does. But generally speaking, there could be three major reasons for your sleeping problem:
First, anxiety or depression: it is highly likely that mental stress will lead to physical dysfunction of your body. And one of the common symptoms resulted from being in a stressed condition is insomnia. You should assess your stress level in recent days and judge for yourself whether your sleeping disorder has anything to do with changes in your work and life. If so, then you should go for psychotherapy, because, as I see it, one month is not a short period, and it seems that you might have some trouble dealing with this situation by yourself.
Second, sleep apnea syndrome, or sudden suspension of breathing during sleep: I think this is unlikely to be your case, since you only started to experience early awakening recently. But the chance is still there. And this is an easy one for you to judge, just ask yourself: are you brought out of sleep due to difficulty in breathing? If so, seek medical help as soon as possible, because sleep apnea syndrome could be potentially dangerous for your life.
Third, hypoglycemia, or low blood sugar: when you are asleep, your brain is not really at rest. On the contrary, it is busying transforming your short-term memory into long-term memory during your sleep. The brain needs glucose to function properly, if there is not sufficient glucose in your blood when you are asleep, your brain will call you up. Do you feel hungry when you wake up at 3am? Even if not, I still recommend you to try eating some healthy snack before you go to bed and see if your sleep improves. Sometimes, hypoglycemia, especially during sleep, does not manifest itself in the form of hunger.