No weight loss since April

Hi everyone

I started working on the new me last August. I was doing real well; I started out at 320 and managed to get down to 255 at one point.
Since April though I have yo-yoed and today I am at 263. While 57lbs in a year is good I know I have more to loose and would love to kick start this weigh loss again. I have been watching what I eat and working out (spinning, weights and cardio) but I am not going anywhere. I understand that it could be a plateau but can they last 6 months? I am starting to get very frustrated now with it.
Did this happen to anyone here and how did you get over it. BTW Male 48 and 263 lbs.

Thanks

Sean