I m gna be honest it depends. Older u get harder it becomes to get pregnant. As age grows egg quality drops. For normal women under 30 have chances of becoming pregnant within first 6 months. If it takes longer then two yrs doctors always to start fertility treatment because at tht time u have much good chances of becoming pregnant. Womem with pcos often have problem becoming pregnant and 40-50% chances of misscarriage. I m 23 i started medical treatment at age of 21. I got married at age of 18 n hlf i tried for two yrs. Thn me n my husband decided we r not going to wait to start treatment. I fell pregnant last yr but ended up with mc i was taking clomid and metformin. It took me 6 rounds of clomid. I m pregnant again with 4th round of clomid and metformin. In two yrs time i changed my diet lost nearly 25kgs. Put myself into normal bmi. Moved out into my own house. Relaxed myself. This all helped.
I always recommed my friends n family never wait too long to start fertility treatment. Because older u get harder it become. U should consult ur doctor and ask him to offer u other treatments such as iui and ivf. Change ur health style if u r over weight loosing it will help alot.
I'm so very sorry for your loss. I can't tell you how long it will take to become pregnant again. Has your Dr tried running any tests? Do they know what caused you to go into preterm? If you haven't got your period yet, I would ask your Dr to do a beta HCG test just to be sure. Best wishes to you and let me know if you have any other questions.