Iregular period, do i ovulate?😭

How can I tell I'm ovulating when I have an iregular period? I sometimes have my period for up to 15 to 18 days and then only 1 or 2 weeks without and I get it again.. I've had enough to say the least.. we want to try for a baby soon but I'm here thinking that it will never happen because I don't know if I even ovulate, I've tried the ovulation test kits but they are just to expensive and I just can't afford it

Has anybody else had the same problem and still fallen pregnant without any help? Or is there anyone that may be able to help me with this one, thnaks in advance