Pain in leg for weeks now there is a hard purple pea sized lump on front of knee with redness. negative us and d dimer. could it still be dvt?

NO: DVT as a rule do not occur on the front of the leg. This pea sized area could be a small node if located on the front of the leg. If there is pain and redness it needs treatment ans see your doctor. If over the knee cap itself it could be a case of bursitis. Please see your doctor soon and do not open this up or manipulate this.

Not likely: The description is not consistent with DVT, and a negative D-dimer makes it very unlikely that you have a deep vein thrombus.