Welcome to the site.
Labetalol can have some effect immediately but for most people it will take about 2 weeks to really 'load up' in to your system. Then it may be a case of tweaking the dose until the blood pressure is responding but without overloading you so that you feel grotty with side effects.
If you are pregnant or breast feeding there are only a few medicines which are safe & licensed to use so if your BP remains uncontrolled it might be worth thinking about lower doses of 2 medicines that very high doses of just one. There is very good evidence to show that this is most effective at controlling a persistant blood pressure but with least side effects.
I hope this helps but do let me know if I can offer you further information or support.
Every Woman is entitled to understand what happened in her pregnancy when pre eclampsia strikes. I hope to be able to support that process.