You can only be entered in a Mega sweepstakes once for that sweepstakes's time-frame. Or, once every week, depending on the sweepstakes time-frame.
Please Note: MEGA Summer 2019 is now over. Stay tuned for more updates and for MEGA Summer 2020.
So for example, The "Your Grocery Bill Paid for 6 Months" sweepstakes ran for 1 week, from June 16h to June 23rd. If you were to win 2 or 3 Mega #OhmHours during that time, you'd still only be entered once for that 1 week sweepstakes, and once for the Grand Prize sweepstakes.
Once that current Mega prize's 1 week time-frame ends, you'll be able to qualify for the next prize, and get another start towards the Grand Prize.