Purely as a personal opinion (not been playing long enough to know anything else) but it might be worth looking back over the hand histories of the sessions where this has happened if it is a pattern that repeats regularly. I'll be getting poker tracker when the BR gets big enough but the trial version might give you some insight into what's happening.

If it's just because your style suits coming into new tables then why not work like that, stay for a while, get the wins and then switch tables. If it's because your concentration slips after a certain period of time then that's different and maybe a switch of tables with a break in between will help?

As i say, just my opinion.