Hi and thanks for your question,
Adenosine, the drug used during the study is a neurotransmitter. Common reactions to this drug include: flushing, difficulty breathing, chest pressure, nausea, lightheadedness, and headache. It's half life is less than 10 seconds. Half life is the time it takes a drug to decrease by half in your body. So it is likely no longer in your system at this point.
Did they give you any other substances before, during or after the stress test and are you taking any medications right now? I would advise you to check with your physician about your plans to become pregnant at this time.