It's pretty hard to make yourself look bulky, if not impossible, so give weightlifting a shot if you enjoy it! I've been doing it for two and a half years (off and on) and I'm still faaaaaaar from bulky, though I have gotten pretty toned!
And are you actually losing weight, so that it's causing you concern? If so, I'd check with your doctor to see if there's a reason why it's happening, as you don't want to adjust your eating/exercise habits, only to find and fix an underlying cause, then end up putting on too much weight after as a result.
Best of luck!