Performance decrease after upgrade

[e_iudica]

Greetings. Yesterday I upgraded to Magento 1.9.1 (from 1.8.1). The only issue is a significant performance decrease.

I've tried flushing the cache but had no effect. However I've noticed that sometimes, when I reindex, the website goes smooth as always for a while, then slow again. My site is www.mondofumetto.com . What can I do?

Thanks for you help.

[e_iudica]

I've compared it with an .htaccess from a clean installation and it's the same. Also, I've tried editing it as usually suggested for increasing performance, but had no benefits :/

[senthilms]

You can try enable slow log which will tell you the exact reason for the slowness. Sometime it could because of a an extension you might be using in your webstore.