advice?

Rachael 🇬🇧 • 👶🏼✨ Baby Boy Born 17.01.19 💙🌈 💙
I don't no the exact day that I had my miscarriage, so in order to work out how long until my next period do you work out from the first day of bleeding or the last day? 
I started bleeding on 3/9 
I bled on and off until 4/7 
So would I work out that it has been 8 weeks since miscarriage or 4 weeks? 
My HCG levels on 3/30 were 70. 
On the 4/11 I had a negative pregnancy test