Ways to Avoid/Break Plateaus

can I ask WHY I have to avoid plateaus? I mean I lost 35lbs despite the fact I never believed I could lose 5. I'd like to lose more but have plateaued or been up/down a few for about a month or two now... my question is why stress about it? I want to lose more and I joined a gym yesterday--wuhuuu-so after a year I think I'll be more serious about working out and not just dieting... but what's made this journey so good and yes, fun, is that I'm not stressing.. I'm eating all the foods I love...still getting results over the last year...buying new clothes... and things are OK. however.. i like all your tips