hi lulu!
i'm not an expert but i would encourage you to exercise anyway... you will find it a lot easier to lose weight if you are burning calories and toning muscles as well as watching what you put into your body. if you're really worried, focus most of your workout time on cardio and you should start losing ASAP.
sometimes i gain a bit if i've been doing tons of weights, but i don't see it on my body. you will lose inches faster if you exercise, even if the numbers on the scale convince you it's not true.
i have a lot of friends that shy away from weights or toning exercises because they are afraid to put on a couple of pounds. but i always think a toned, thin body looks better than just a thin body- and the toned body works more efficiently.
but that's just my opinion! i'm sure there are lots of others here who will have different advice for you