Rapid weight loss and increased appatite, feeling dizzy and

i have had the pill injection 6wks ago, i was warned that i may put on weight. i have lost a stone in a week and am slim anyway. i had a funny turn last week where i nearly collapsed and went yellow all over my skin. i get sweats and fast heart beat. i have had bloods done and had an ECG but all came back clear. i am either constipated or have loose stools yellow or dark...no in-between. i get a stiff neck a lot. when i eat it feels like i have a hole in my stomach where the food is just falling through, i get hungrier as i eat and even when i have had a massive meal i still feel like i have an empty belly. i am 26 yrs old and have a toddler and baby to look after 24/7, i cannot go on like thins anymore, the doctors are not sure what is wrong as my bloods came back clear.
Please please can anyone shed some light on what is happening to me as it is really starting to scare me now.