Question about blood clots or dvt. Please help?

Ive taken two long car rides one on Friday and one today. The first one was 13 hours and the one today was about 10. I got out several times and walked around and have also taken out asprin throughout the day. M left thigh is kind of burning feeling and down the back feels sore. If I pull my knee to my chest I get pain down the back. I've had 4 dopplers done in the past which have all been negative as well as negative d dimer tests. I have a phobia. Should I be worried now?