What are possible consequences of having enlarged lymphnodes in abdomen for months?

Usually none: A correlation with your symptoms is required. Unless this is a workup for fever of unknown origin / weight loss / night sweats, it's unlikely that biopsy of these nodes will be helpful. You're a young man in what should be your physical prime, and lymph nodes are often big at this time in your life. If your physician is not concerned, you should not be either.