M/36/175cm [104kg > 71kg = 33kg] weight loss prosess

So, I used to weigh 104kg, but now I'm down to 71kg. It took me about a year and a half to shed the pounds. Now, I'm wondering if I should start bulking up. Also, what can I do about the loose skin on my belly? Can I tighten it up, or am I stuck with it?