If you can find one in your area, you should try to see a doctor who's a concussion specialist rather than asking people like us on the net. There is a standard questionnaire that you can do to get some idea how severe your effects are:http://www.cces.ca/files/pdfs/SCAT2%5B1%5D.pdf
I had a big crash in 2010 and a sports med doctor gave me the test three times, starting about a month after my concussion. I also talked with the physio who was working on my back (broke a vertebra in the crash). He works with the national team speed skaters and had lots of experience with them suffering concussions at events.
Without trying to prescribe anything, I'd say that you should be very cautious about getting back on the bike soon. My concussion was bad enough that they put me through CT scans three times (twice at the hospital in Italy, once after I came home). It appears as though concussion effects are cumulative and if you have residual problems from your first concussion, it can mean that another bump on the head can be even more severe. Yes, you want to get back on your bike but you only have one head. Read some of the reports of long term effects on football and hockey players and you might decide to stay off the bike.
My doctor allowed me to go back to moderate exercise where I had no risk of falling (i.e. trainer) after about six months. A while later, he said I could ski as long as I didn't hit my head. Of course, on the second run on the second ski day, I was going down and made sure I didn't hit my head. However, I did manage to dislocate my shoulder. It was exactly ten months before I was back on the bike. I went back to work after about a month (part time since I'm semi-retired). If I could go back I would have avoided work and moving pictures (TV, movies, etc.) for at least another month since I had moderate symptoms for two full years and wonder if I'd have been better if I'd taken more time off.