^Medicine does expire, it just takes a very long time; certainly longer than weeks.
OP, injecting that pill is a huge mistake. Aside from the already proven dangers of parenteral pill use, it's been sitting in god know's where collecting bacteria and other nasty shit. We've all done crazy things, but have some respect for your body please. If you continue along this line, you're going to be looking at abscesses in the least and possibly more serious consequences... systemic infection, staph, MRSA and what have you.