Doing very poorly in Call of Duty: Modern Warfare 2 - Multiplayer?

I used to get KDRs of around 10:1 and 20:1, double pavelows here, constant double harriers there, now all of the sudden I can barely manage a 1:1 KDR. I don't understand, my last KDR was 35 kills, 4 assists, and 6 deaths, and that's the best I've had in probably a month! It's really bringing me down, not to mention it causes me to notice bothersome players (tac knife spammers, tubers, glockers, etc) and eventually become a very bothersome whiner. It really brings my mood down. I feel like my assault rifle only does about 10 damage per shot rather than its supposed 30 damage, and have to resort to secondary up-close weapons such as the M1014 to get a barely decent KDR. Does anybody know why this might be, or how I can fix it? I use the same weapons I used to be great with, but I can hardly even aim with them. I feel like everyone has twice or three times the damage my weapons have. It's really bothersome, and I could really use some advice.