Any suggestions for knee pain while sitting criss cross or with my feet under my .?

I am 21 and I was a competitive cheerleader and gymnast. I have had several knee injuries but after I sit criss cross for literally less than 5 minutes my knees are throbbing and I am in serious pain, with swelling. If I sit with my feet under my I am in the same situation with major pain and swelling. Does anyone have any suggestions other than the obvious "don't sit like that". I have stopped sitting like that but my knees continue to hurt and regardless I don't think it's normal to have pain at 21? but maybe it is...?. FYI... it's both knees. Main pain comes from knee cap and surrounding areas. Any feedback would be appreciated! Thanks!!! :)