At this stage, you should not focus on being a marketing consultant. Instead, you should work on getting an entry-level position in marketing, as an employee.
Before your ego protests, tell yourself that you are, for now, only technically an employee. You will act as an internal consultant.
Work smartly for at least 3 years: don't keep doing the same tasks, but stretch by asking for difficult assignments in different areas.
Think both process and content. For example, you might be assigned to create and test a Facebook Ad. That is the content. Pay attention to the process of how you do those tasks within your company. Is there a more efficient way to get it done? That is process.
After 3 years, keep working until you start to feel bored and confined at your company, and don't feel like you can grow anymore—that is the time to leave and become a consultant.