How could I motivate myself to lift weights and exercise?

I used to do heavy weights but after a week or so I got bored because it's boring. For example I do around 100 pounds on each side and after around 12 reps I get tired and have to rest for like three minutes before doing 4 more sets, which is really boring. At the same time my mind is feeling lazy. I have school in two more months and it's just saying "There's no need to exercise, not like you're going to get any results in these two months" and so on. So, how could i motivate myself? I've been feelign really lazy and just playing my PS3 all this time.