Why did I receive over 900 dollars in education credits last year and only 100 this year when I am in the same graduate program?

Lifetime Learning Credit is a non-refundable credit that can only be used to reduce your tax liability to zero.   If your liability was less for this time, that is why the credit is less.

If you claimed the lifetime learning credit and you had tax liability last year of $900 and this year of only $100, then this would be the reason you received less this year.  This is a  nonrefundable credits.  This means if you look at 16 of your form 1040, the amount of your credit will not be greater than this number.  It is also possible that you had other credits that offset your liability first.  If so, if you look at line 24 and this is $0, this would be the reason your Lifetime Learning Credit is not greater than $100.