Period problems

Okay so I haven't had my period since October of 2014. I'm not pregnant but we have been trying for about 2 months now. My period isn't regular but how am I to know if I'm pregnant if my period comes when it feels like it? Somebody please help! I would really like to stop spending so much money on pregnancy tests and just be able to know if I'm pregnant or not. And if you have any advice on conceiving please let me know. Thank you.