There's no scientifically-backed method to determine the gender, save for an ultrasound. I have 2 boys and endured morning sickness and heartburn with both of them. Both of them had heart rates that hovered around 160bpm. They each carried differently, my belly "shape" was different both times, and I craved different foods with each of them.
There is one you can do for fun that I have yet to see be wrong, but remember that it's noooo guarantee.
Stick a threaded needle into the middle of an eraser on a sharpened #2 pencil and have somebody suspend it over your wrist (about 1/2" or so above) on a solid surface like a table. It'll start to spin in a tight circle back and forth and then it will swing. If it goes back and forth in a straight line, it's a boy.... If it makes a circle it's a girl. But here's the catch.... It will tell you EVERY baby you're going to have, in birth order. It also includes miscarriages and terminations into the order (kinda creepy, right?)
If you're gonna have more than one the pencil will return to center and do the first style of spin again before swinging for the next baby. You'll know it's finished when it does the spin for a long stretch (like ten seconds or so), and then it will start the sequence all over again.
Like I said, this one is just for fun, but I have yet to see it get somebody wrong... Lol. Oh and if you try it on a boy it will just twist back and forth and act all crazy. :D
It was true for me... on both counts! But, they're wives tales for a reason... sometimes they're bound to be true.
I think the body does have a different reaction to opposite genders... I exprienced it, but it can go either way. I happended to have no morning sickness with my boys and had it with my girl... but it could go opposite. For me, my boys pregnancies were similar and my girl was different.