Since you are experience a recent infection we nees to consider the vital configuration parts.
AVG Free/Pro or IS will do fine already as primary realtime protection, meanwhile on demand scanners are useful to scan them once a week follow the suggestion as mentioned.
Backup are really a must with your External HDD and program like built in windows or third party will easily accessible in case of emergency happen.
How do you expand a lot? Many extension may cause slowdown through browser operation.