lightheaded, dizzy, and nausea??

are these things normal during the third trimester??? i started feeling lightheaded when i got to work and i felt like i was really out of breath... then i felt a bit dizzy like if i didnt sit down, i would have definitely fallen... so i sit down on a bench for a minute and out of nowhere, i just threw up... the exact same thing happened to me when i was 20 weeks pregnant.. and i was fine.. but now my mom is freaking out telling me to call my doctor.. i literally feel completely fine now.. and i have an appointment tomorrow but she still wants me to call..