Find another club where they won't injure you!
It is very bad form for your sensei to injure you - I would be quite distraught if I did this to one of my students. How the heck did you get injured from yonkyo!? Is it the rolling/flipping?
Really you should see a doctor (is there no one you could pay for a single visit?) Alternatively I would stop training if the pain is bad. You could try taking cod-liver oil (or glucosamine is very very good for joint problems and very effective but quite expensive), though it could be a ligament problem instead. Basically rest it - I've had a painfull elbow from stressing it in the wrong direction (do you do shiho-nage where you have to flip over?) - after around 8 weeks of rest it was OK.
Also, will your aikido insurance will cover medical costs? If you do not have aikido insurance this suggests your instructor is very dubious.
In our dojo we have a risk assessment procedure which means that all injuries have to be recorded, and any methods to prevent the injury in future have to be instigated.
Be careful out there!