Hi LittleCharmer...
Suffered a bit from this too. I have a history of tachycardia and while I am asymptomatic at the moment, I've had weird moments where things don't feel quite right, usually if I'm moving around a lot, lifting or getting out of a chair. I am 8 weeks today.
From what I've read, the volume of blood in your body increases quite a bit during the early stages, causing your heart to have to work harder. Apparently it's quite normal to get a bit more out of breath than usual doing things like walking up stairs.
One of the worst things I've found about the early stages has been persuading medical professionals to take an interest before my booking appointment ( still have a week to go). I'm having other problems too, mainly with depression and anxiety and am having to be very persistent to get any help or information.
You know your own body better than anyone. If something's not feeling right, remember you are entitled to ask your GP, Midwife Service or local Early Pregnancy Unit for help.
Don't panic ( most likely you are fine and being anxious makes everything worse ) but do get checked and keep asking questions.