I've been pregnant before but now I can't. My cycle is 21-24 days and my period is 2-4 days. Is there hormone problem? How do I sustain that?

See your OBGYN. U need a workup, u need blood work exam, cultures and u should be doing an ovulation test at the proper time to see if u are ovulating and u may need other testing such as hsg, etc. At 24 yrs old u should be able to get preg if nothing (which you have something) is wrong.