Hi there! I had the same problem. Do you have any other personality traits that go along with this? Is there any reason you can think of as to why you'd be reluctant to look people in the eye? In animals, it's a sign of confidence and standing your ground. To humans specifically, we use it as a sign of respect in some societies and a sign of power/seniority in others.
Practice in small amounts. A little longer each time. Realize that we don't maintain eye contact the whole conversation, we look at other things and look away (otherwise we are considered threatening or... there's also a romantic implication, if with a special someone). When you walk around, practice keeping your head up. Try making eye contact with those you know or are in a friendly setting with, supply a smile and a greeting. The more positive experiences you have with it, the easier it'll get. Little by little!