Suggest changes in my itinery for a smooth trip

Hi nikita123! I think your itinerary is very ambitious. You should check traveling times using the timetable for the trips you've planned, as that will give you an idea of how long your journeys will take. For example: both Bern and Geneva on day 3 would be too much. So are Gstaad, Montreux, Vevey and Glacier3000 on day 6. A day trip to Lugano from Interlaken isn't a great idea, as a single journey takes 4 to 5 hours. I think you can better focus on the regions around Interlaken, Lucerne and Zweisimmen/Gstaad during your stay. There's so much to see and do there that, especially directly south of Interlaken, that you won't get bored at all. Browsing the forum and searching through this list of day trips may help you out.