Is it normal for my scar to be hard and lumpy?

Thanks for your inquiry, but without a picture it is hard to advise.  My suggestion is for you to re-post with some pictures so we can comment.  

It can take over a year for scars to fully mature. In the meantime, especially at only four weeks out, firmness, lumpiness, etc., is expected. Some of it is dissolving stitches which may take a few months to fully dissolve. As well, the scar will soften, and relaxes over time. Keep in close contact with your plastic surgeon to monitor your progress.Best of luck!Dr. SubbioBoard-Certified Plastic SurgeonNewtown Square/Philadelphia, PA

Thank you for sharing your question.  Initially after surgery incision sites can be firm and slightly irregular as your body is trying to heal and placing scar tissue to do so.  This scar tissue will flatten, soften, and fade with time but there are available treatments to help improve the appearance and speed this process.  I am attaching a link below that should provide additional useful information.  Hope this helps. 

While it's not the norm, many people will still have a lumpy and firm scar at only 4 weeks after their tummy tuck.In many cases it's simply part of the healing process and can be related to the body's reaction to the absorbable sutures that are utilized in surgery.  I would recommend scar management with either silicone sheeting or a moisturizer with mechanical massage to the area.  It can take up to 3 months in my past experience to improve.  If it seems to be worsening it can be the beginnings of hypertrophic or keloid scarring.  In that case I would see your Plastic Surgeon sooner rather than later.  

It is common for the scar to feel hard and irregular at 4 weeks.  The tissues are still swollen and the underlying sutures are not yet dissolved.  This will soften and irregularity will smooth out over time.  Massage can be of benefit.  Good luck.  Donald R. Nunn MD  Atlanta Plastic Surgeon