tired by mid afternoon

Hello ive posted before and got very good advice,so here we go again..Im type2 newly diagnose sept2008,im on metformin 2x 500mg twice daily and also recently taking losartin25mg once a day.On low carb diet which is really successful for me lost oodles of weight .bUT recently have been feeling really exhusted mid dayish yesterday around 2pm had to have nap in my car cos so tired,so im quiet concerned,Do u think i need to have metformin at lunch too or is it the Losartin?I used to feel so tired before i was diagnosed with diabetes and after taking Metformin and exercise weight loss etc felt really good good now im tired again.Recent hbc1 was 6. and GP said ok.Any ideas please...........Wendyb