I'm 5 Weeks Pregnant But I've Had Two Miscarriages Before

I'm 5 weeks pregnant but I've had two miscarriages before this. So I was placed on progesterone injection but started bleeding this morning and my doctor said I should take primolut depot injection and be on bed rest. The blood is not bright red but very dark brown and kind of thick should I be worried that I'm losing this one too? And what can be the cause