*SNAP* I was about to say exactly what Mel said..... LOL!

I have the same thing, if I haven't had a snack (like a peice of fruit or a sweet biscuit or sugary drink something) in 2 hours I start to get very very faint and dizzy. I have very low BP though as well. It takes me a while to get round our shopping centre too, as I sit at pretty much every opportunity! Try carrying some snacks with you, or a cold sweet drink, when you go out and take a bite/sip every 5 minutes or so and see if that helps.