After some rough sex i developed a thick cord on top of my penis, it wasn't painful but wanted to get rid of, someone else recommend arnica gel, i applied this to my penis on 28 dec and 2 weeks later penis is still burning and painful - what to do??

That thick cord on top of your penis very likely could be thrombosis ( blood clot) of the dorsal vein of the penis caused by trauma during rough sex. Consult a urologist ASAP for accurate diagnosis & proper treatment. In the meantime take an adult aspirin. You can apply the gel also. Is a STD a concern here as well? If so, mention it to the doctor.

Clean the area with soap and water and apply cortisone ointment till it heals. Pl. never treat yourself with suggestions of well meaning friends- it is dangerous. The hard area will subside slowly with time. Hope you do well