Do you happen to have Origin in game enabled (it's enabled by default) as it causes low FPS and sometimes lag. If it is enabled disable it and try playing again to see if the problem persists. Does the FPS problem happen in other games, are they just origin games or games from various publishers?
If Origin in game is enabled, disable it. To turn off Origin in game log into Origin, in the upper left hand corner click on the word "Origin" in the menu, and then click on "Application Settings". Next go to the "Origin in game" tab and uncheck the "enable Origin in game" box.
Minimum requirements for Battlefield 3
• OS: Windows Vista or Windows 7
• Processor: Core 2 Duo 2.4 GHz or Althon X2 2.7 GHz
• RAM: 2GB
• Graphic card: DirectX 10 or 11 compatible Nvidia or AMD ATI card, ATI Radeon 3870 or higher, Nvidia GeForce 8800 GT or higher.
• Graphics card memory: 512 MB
• Sound card: DirectX compatibl sound card
• Hard drive: 15 GB for disc version or 10 GB for digital version
Recommended system requirements for Battlefield 3
• OS: Windows 7 64-bit
• Processor: Quad-core Intel or AMD CPU
• RAM: 4GB
• Graphics card: DirectX 11 Nvidia or AMD ATI card, Nvidia GeForce GTX 560 or ATI Radeon 6950.
• Graphics card memory: 1 GB
• Sound card: DirectX compatibl sound card
• Hard drive: 15 GB for disc version or 10 GB for digital version