can anyone tell me about how this holiday weekend will affect my trip to italy( rome and sorrento),and switzerland(like museums etc).thanks

Whit sunday and monday is Pentecost in the church year. Pentecost was two weeks ago. When are you travelling? Yes, it does affect stores and museums - you have to ask what is closed. I have been in Norway and Paris on WhitSunday and it did affect what I did.

Both days are generally holidays in Europe (not UK or Ireland). Monday is a holiday in Switzerland, but not in Italy. General opening hours apply, but when museums etc are normally closed on Monday, they often stay open for Whit and close another day instead. Shops will be closed (except tourist shops), but restaurants should be open. Many European schools get a week off for Pentecost and many families travel, putting strain on roads, rail and accommodation, so you want to reserve well in advance.

next year===I am going the friday before and the week after and I was interested in going to the vatican museum and othe sites in rome and pompeii and the naples museum. is the holiday week before or after????

In many countries in Europe schools have an Easter holiday of two weeks, and only the Monday off at Pentecost. Some parts of Holland have a week or two weeks, often including Ascencion day weekend as well (this is from Ascencion day on Thursday through to Sunday).