Sorry i meant meds. not mess.
The same thing happened to me at 4 weeks, ended up I had an infection. The doctor gave me mess and I was sure to drink plenty of fluids. You might want to go to the Doctor of the pain continues. Best of luck to you!
I think it is normal to have SOME period like pain whilst pregnant, around the time your period would have been due. Plus there are pains when the uterus starts to expand to allow more room for baby...though i think this is usually later on. If the degree of pain you're feeling worries you, maybe a call to your dr would be a good idea?