Slow item fetching

Hi there,
I have been using erpnext from past 4 months and all was working well recently i have crossed 1000 items and now when i create a sales invoice i use barcode scanners it takes a lot of time to fetch the item i scan 4 tins pop up shows 4 times but the child table sometimes has 3 sometimes has 2 in it,
Please help me solve this issue its very frustrating and also suggest me ways to soeed up scanning process
Thankyou in advance