You can't unless you run two lines. You should be using 12/2 to bring power to one switch. Then you will need at least 14/3 to run the two travellers and one common to the other switch. From the other switch to the load, you can use 14/2.
You CAN wire a three way switch with 14-2. You run a 14-2 cable from the lightbulb to one switch and connect the black to the bulb on one side, and the common connector of the switch. The white wire is unused. Run another cable from the bulb to the other switch, also connecting the black to the common on one side, and the bulb on the other. Finally, connect neutral and hot to the remaining poles.
The downside to this is,if the light is off it can still be hot on both sides of the circuit. It's probably not up to code either.
Wiring a 3-way switch can be intimidating. It's easier if you look at a diagram of it's operation on a site like "wiringhelp.com" before doing anything. Hopefully the instructions are still inside the box with your 3-way switches (it's a special switch). You will have two traveler wires where either one could be considered HOT. It's a good practice to mark ANY wires than will be used as the HOT wires with a black sharpie or magic marker so it can't be confused with a common (white) wire should someone else follow your footsteps. It doesn't hurt to have a visible voltage sensor (available for about $15 to be sure the power is off-or to identify which wire is the source HOT wire should things get confusing. Good luck.