Taking PrEP while not knowing that you are HIV positive is bad for your health. PrEP provides a low dose of antiretroviral treatment (ART). With good adherence, this amount of ART is enough to stop you from getting HIV, but if you already have HIV it could make you more likely to develop HIV drug resistance. This is where your ART stops working. Small amounts of ART are not enough to stop the virus from replicating, instead, the HIV virus is able to change itself so that it can by-pass the effects of ART and create new copies of itself anyway.
Testing regularly while you take PrEP means that you will find out if you are HIV positive as soon as possible, so you can avoid developing HIV drug resistance. Taking PrEP as prescribed will prevent you from getting HIV.

Yes! PrEP does not stop you from getting pregnant and is safe for women to take during conception, pregnancy and breastfeeding. PrEP is one of the ways that couples with different HIV statuses can try for a baby safely.
If you want to have a baby, but think you're at high risk of getting HIV, then PrEP might be a really good option for you. If mothers get HIV during pregnancy and breastfeeding, it puts their babies more at risk. This is because your viral load is especially high in the first few weeks after getting HIV. Taking PrEP protects both you and your baby, so you can stay HIV-negative throughout conception, pregnancy and breastfeeding.     

People have different experiences when taking PrEP. Many people have no troubles, while others might experience things like nausea, vomiting, fatigue and dizziness, but these usually disappear after about a week or two.
Longer-term effects of taking PrEP are rare. Around 2% of users may have small decreases in kidney function, but this usually returns to normal once you finish taking PrEP. This is why it's recommended that people on PrEP have regular health check-ups so that healthcare workers can monitor their health.
If someone thinks they're experiencing side-effects to PrEP, they should speak to a healthcare worker.