It could be many things from old pellets to a barrel that was'nt cleaned properly after last season. First check to make sure your barrel is fine. What did your bullet powder primer combination consist of last year? is everything the same? A 3" group is'nt that great at 100yds to begin with, mabey you had problems last year and now there getting worse.
Loose powder is the best way to start off, start with 90gr's and work your way up in 5gr incriments untill you find the best most accurate load, it usually falls inbetween 90-110gr's of powder, and remember NO COFFEE befor you shoot.
Success to you!
(BP)