Doxycycline Hyclate and dilema

I take doxycycline as an anti-acne medication. I've been on it for two years now, with an increase in dosage from 50 mg 2 x a day to 100 mg 2 x a day.

If I take it without food, I feel incredibly nauseous, so I'm careful to take it always immediately after meals. My prescription says do not take within 2 hours of eating dairy products, but sometimes I can't avoid that, since I have to take it with meals... I am also a lot more prone to sunburn since I started taking this, including one really horrible sunburn I got in FEBRUARY last year! ugh!

Does anyone know if there is a limit on the number of years one should take this medication for? Having been taking it for two years now, I began wondering if there could be negative consequences to the drug being in my system for such a long time without break. I am going to ask my doctor the next time I go in for a visit, but wanted to try to find out on the 'net first.