What are the causes of infertility in women at 28?

Different causes. Couls be problem with ovulation, tubal blockage or abnormal sperm. Sometimes infertility also tends to be unexplained where we can't find a reason.
Infertile @28. Wow! many reasons: 1. Anovulation of various causes, pco, hypothyroid, anemia, etc. 2. Obstruction blocked tubes 3. Immune endometriosis 4. Male infertility 4. Genetic 21-hydroxylase deficiency, premature ovarian failure. Whew!
Many possible causes. The most common causes are: low egg supply (diminished ovarian reserve), problems with ovulation including polycystic ovarian syndrome (pcos), hormonal problems like thyroid or prolactin issues, damaged or blocked fallopian tubes, endometriosis, fibroids or polyps inside the uterus, and/or sperm problems. Less common - low hormone levels or problems with the cervix. See a rei specialist for help.