usually around 14 dpo you will get a for sure answer .. however some women have gotten early positives around 9 dpo so it's kind of up to you if want to start testing early just keep in mind that testing that early your HCG levels may be to low and you will keep getting negatives ... Good luck though :)
Hmm this is tough because everyone is different! When i was pregnant i tested at 8dpo and 10 dps with early tests but the were both negative. I didnt get a positive until 12dpo and that was with clearblue digital. Theoretically you can get some tests that will give you a positive 8dpo but these are only accurate in about 60% of pregnancies. I would say maybe get some cheap tests u can buy on the internet that are early response and try every day from 8dpo but be prepared to get negatives until about 10-12 dpo. If u only want to get the expensive tests then i would wait another week to test.
Good luck!