Why did they lock you up? Prison or psych ward?
It sounds like you need medical attention, and youre obviously concerned - that's why we're all saying the same thing. You know better than we do how serious or urgent it is...
IV heroin use can have a number of serious complications, it's pretty important to get any health that arise issues seen to by someone who can determine what the matter is.
Can you get to a doctor or hospital - doing whatever it takes not to get locked up?
That's really the only advice I think we can offer you - it would be irresponsible for anyone here to give you health advice.