Going from a 10kg bar to an olympic bar will really change the lifts, especially if the oplympic bars are longer than the 10kg bar.
I noticed differences when I changed gyms about two years ago. the bench at my current gym was softer and lower than my old gym and it felt really strange, like I was on decline or something.
Deadlifting your going to have changes in knurling and bar circumfrance.
Squat, again the bar length will have an impact and also the didstance of the rack from the wall/mirror you are facing can throw you off.
Of cause these are minor things which shouldnt make too much difference unless you are very experienced and moving BIG weight.
The biggest factor as others have said is probably a phycological thing of not being as comfortable in the new gym. Also if you have made other changes like moved house or changed your schedual you might just have a bit of stress and its not allowing you to train optimally.
Bottom line is that its normal and probably wont last more than a month IMO