welcome to Health care magic.
1.It could be re-growth, reoccurrence if the
lipoma again (its possible in many cases)
2.Or an infection in the scar area with internal collection causing lumpy feeling - generally with pain.
3.Yes it should be concerned, you see your GP and get the area scanned with
ultrasound - it will help us to assess the nature of the lump,its source and extensions.
4.Accordingly the treatment can be planned - if lipomatous - just monitoring is enough, removal upon discomfort.
5.Suggest do not scratch the area,as it may get complicated.
Hope it helps you. Wish you a good health.
Anything to ask ? do not hesitate. Thank you.