1st day dark/black looking blood. period last 3 days not eve

i usually have very heavy periods the first couple of days. and my period lasts for 5-7 days. Sometimes irregular else ok...

I'm a gym fanatic and due to some upcoming events, wanted to work out even harder- i am at a healthy weight and the doctor prescribed Duromine (makes you not hungry) which i took daily from last week and coupled with soooo much stress at work this month - i lost 3 kgs last week

emphasis on stress there :-(

Last month my period was fine. this week it arrived at the expected time- first day because i didn't have much i left it on the whole day (the pad)- when i checked at the end of the day- it was very dark- almost blackish looking...when i wiped- looked kind of dry....
the next day i had the normal red color- though very light (when it should be heavy usually). the day after- pretty much nothing (except when i go to the toilet, wipe and may see some blood or abit of blood/clearish discharge) - else thats it.

should i assume that thats due to the stress/too fast weight loss? I know there are a couple of other workmates who are either waiting for their period or are irregular- they also say its stress related ... just curious...

Thanks for the reply= just slightly worried :-(