Do you have any discharge or itching at navel?
Any bloating, nausea, gas?
Are you diabetic?
An hernia will give a bulge on cough or straining. In the absence of bulge, just pain will not point to hernia. Pain during these activities you mentioned denote muscle sprain. Warm compresses, local analgesic ointment (cream), abdominal binder, anti-inflammatory analgesics like Motrin (Ibuprofen) will take care of this.
Please feel free for your follow up questions.