I share your pain. My now 7-month old has done the same thing since day one. I was lucky if he'd sleep for 30 minutes (the norm was 20-30 minutes) at a time for naps. His napping improved slightly at daycare when I returned to work, but at home he'd stick stubbornly to those quicky naps. And up until recently, this was how we spent the past 7 months. I asked the doctor about it, and he said as long as he's healthy, happy, and gaining weight and height accordingly, there should be no concern about it. Some babies just don't nap that well, and in all actuality, that phrase 'sleep like a baby' doesn't apply to all babies. . .as we exhaustingly found out. My boy sleeps great at night, it's just that daytime napping that I dreaded. (I asked around finally, and was shocked to learn how many babies DON'T nap that well during the day).
During Spring Break just two weeks ago, my boy started sleeping for 45 minutes to an hour, with the longest stretch going 1 1/2 hours. Going through what you're currently experiencing, I thought something was wrong - he's NEVER slept that long during the day! But he was just tired, I guess. He's also rolling around and commando-crawling around a lot more now, so part of me thinks that since he's more active, he's more tired, and sleeps better for naps. It doesn't happen every day, but more often than not, and now his daytime naps are averaging about 30-60 minutes. . .which, compared to 20-30 minutes, it's a Godsend.
Going through this myself, I don't know if daycare is the culprit, as I said, he's been doing this since day one, before we even started daycare. But he's happy and healthy at daycare, so as long as he seems happy and content there, I wouldn't worry too much about it. . .hopefully your little one will start growing out of it soon.
Go with your gut and take it one day at a time. I know it's hard, but hang in there!