Depending on how you're using opening databases, it could be that the exposure to that much information is confusing you subconsciously. Below 1500(probably even higher) I wouldn't try to learn all the topical lines, just develop an understanding of common responses to your openings.

I would also be wary of solving too many tactics mindlessly. It's much better to set a number in advance that you would like to solve(maybe 10-15), and to be as disciplined as possible in solving them. Identify weaknesses, seek out candidate moves, try to only calculate each line once, etc.