My practitioner told me the pain I'm currently having is due to my pubic bone separating. How can I alleviate this pain?

Not much. The pubic bone commonly stretches before pregnancy. Thank goodness otherwise no one would come out vaginally. Some women have an excess separation after birth that can cause difficulty walking. Rest and time are really the only things that will lead to it healing.
Avoid pelvic stress. As the term of pregnancy approaches, the cartilage layer connecting the pubic bone softens. This can increase the potential diameter of the pelvic outlet which is an advantage during delivery. The only thing you can do to reduce your discomfort is to avoid physical activity that may cause stress on this area, such as quick twists or jumps. Be guided by the paid and avoid what causes it.