Cogga, he is very young to have nightmares. It might be due to something else like an ear infection for instance. The best would be to take your little one to the doctor and make sure that nothing else is the matter.
Although there is an association between nightmares and stress and anxiety, it usually is the stress and anxiety associated with normal life and there isn’t much we can do about it. If your child awakes crying/screaming, go to him quickly, hold him, talk soothingly and reassure him that he’s safe. You can also try getting a night light and see if that doesn’t work. Unfortunately there isn’t much more you can do and hopefully it will go away by itself soon. Good luck.