how much can i loose in 16 weeks

so i had lost some pounds felt grate looked good i was happy ..then i stoped using this and i stoped working out i gained it all back :( .. ill be 21 in16 few weeks and want to feel and look how i used to when i was at my helthiest .. i love advice, exercise tips anything that could help me :) im in college im an RA with a second job so it hard to balence life! i need all the help i can get ..do u guys feel this way ?