Since you have completed your graduation its less likely your IQ is below normal range otherwise you would not have come this far in education.
Next about mathematics problem its a chance you are suffering from Dyscalculia
(specific learning disability
) but if you dont have to worry about it as well if you dont deal with mathematics which cant be done with help of simple calculators.
Thirdly, forgetfulness and lack of concentration if present since childhood along with loosing things, clumsiness, hyperactivity and impulsiveness; then Attention Deficit Hyperactivity Disorder
can be thought of. However if your symptoms are of recent onset then we think of in terms of stress be the reason behind it.
If you have any anxiety, lack of confidence, decreased sleep/appetite, restlessness
so see a psychiatrist
Hope it helped your query.