Hi,
Hugs to you! What you are going through may just be your body adjusting post baby and post birth control. I will ask though, are you soaking one heavy pad or tampon per hour? If so, call your OB back and tell them - they will get you in immediately - and if not, find another one or check with the ER.....Not to scare you, but just to keep you from too much blood lose that will dehydrate you, possibly give you anemia, etc.....I am a 42 mom of 4, with my youngest still nursing at 10 months - I am also an LC in training.....it has been my experience that periods can return to mamas within a few weeks post birth even with exclusive breastfeeding. Sometimes the hormones just don't play out the way we would hope :) - I can recommend co-sleeping (either in bed, if you are comfortable and safe with it) or baby in the room - also, skin to skin (baby only diaper - mama no top - baby against the chest - blank around both) - this can be nice during nap time - I did this with a sling so that I could still get around to do a few things. This will help increase milk supply and may help regulate your body off of the period. Also, which you maybe doing already, on demand nursing and no or limited bottles until the milk supply is up. Any chance you could meet with a lactation consultant? They could work with you drinking Mother's Milk tea, taking fenugreek and or milk thistle, getting a pump to help bring up your supply, etc.
It is possible that you will still get your period even if your supply jumps up - and you may notice either a few days before or at the beginning of your period your supply will diminish (the baby may nurse more during this time trying to tell you body, hey I'm here! :D) - if this occurs, you can take the Mother's Milk tea, fenugreek/milk thistle, etc....and skin to skin during that time.
Also, if it helps, when mamas can't take the pill and breastfeed I have other LCs and midwives recommend the rhythm method (you check your temperature throughout the month, check vaginal discharge thickening, etc) to know when you are fertile. Just a though if it helps! :D
I hope your ultra sound comes back ok! And hoping all works out well!