My IQ is significantly lower than before. Is there something wrong with my mental health?

Drop in IQ. A drop in your IQ is always abnormal and requires medical care. There are many possible causes for this. Call yor doctor for an examination to find the cause and get proper treatment.
Iq. Not sure when u had your iq tested first and if there is substance use. Best to discuss with whoever did the testing.
Iq. Wonder if there is discrepancy due to different methods used to test your iq, or if there is effect of substances such as pot.