Well if it affects you only in the summer, and you don't have blackout curtains, then I'd think it was a light issue. I remember the first time waking up before 4 a.m. and thinking, "What the hell?! It's LIGHT out already?" My first mission was to purchase blackout curtains.
Yes, I have trouble sleeping all the time, due to stress and lingering pain from an accident. Last night I slept about 4 hours. Some nights I literally don't sleep at all. I've tried several over the counter sleep meds, and even Actifed (sinus med). As Lara said, sometimes they work great, sometimes not at all. It's a toughie.
I've also used a lavender pillow spray that is supposed to promote sleep, "sounds of the ocean" on my iPod, deep breathing/relaxation techniques, anything and everything I've ever read to help promote sleep. I go to bed at the same time every night. Still, I have trouble.