Can you help?

I'm 20 years old and trying to conceive, I know it's a young age. But I'm ready. My periods have always been irregular but I'm very healthy. I've been trying for about 3 months and I have not had a period since but have taken many tests and all negative. I feel nautious at times. And I refuse to eat half the food I love. But the test says I'm not pregnant. Any tips to help me concieve?