Summer is a notoriously slow time on OLD.
Definitely. Summer tends to be pretty bad. A lot of people go on vacation, but they do check their emails, so it looks like they've been on line. I've written to guys, not heard back, and then a few weeks later I would, usually with a "Sorry, I was away..." start.
I would go through "dry spells" sometimes when it seemed like I was sending out a mindless amount of emails and getting no responses.
Just keep plugging away. I met my BF on yahoo, he'd been having no luck either and was ready to bail on OLD and my email got through. Almost 6 months later, we've both canceled our accounts and taken down our profiles!