That drug trial? I'd get in touch with the doctor even if it is by phone or email.

Some drugs deplete magnesium big time. And who knows if this new drug you are on does that? Getting a bruise like this is not common, and also rather scary--- that platelets might be affected. So you need to contact that doctor running your
trial and report this. Others may be reporting it and he might be able to help you with it.

If an artery or arteriole becomes blocked (spasm of the wall or clot), it will back up the venous return in that area, slow down the blood flow and the blood may clot and break a vein. But this is not common.

Magnesium improves blood flow, and relaxes the smooth muscle of the arteries. I am sure you know I have a magnesium thread in Vitamin forum.
It will not do much for your numbness, however, or other issues, but it may help with your spasms.