Hi
You mention you have a discharge. Is it offensive in odour, bloody and how much?
Headaches, nausea, and tiredness can all be symptoms of stress which can dramatically affect periods.
Negative pregnancy tests do not mean you are not pregnant, if you test again at a later date you may get a positive as they work on the amount of pregnancy hormone in your body and in the early stages the levels of pregnency hormones are low.
If you are in any doubt go and see your GP as they will be able to reassure you.
All the best