woolie,
i'm a female paramedic...5' 7" and all of 115 lbs... and i've been doing EMS for 3 + years. it's not bad most of the time. you learn to lift with your legs and find out what works best for you, but some days and some patients will be too much for you. i never try to take on too much...it's better to have extra hands and have to wait a while for the FD or rescue, then to drop or hurt a pt. just imagine the paperwork!!!
females will never be as strong as males (well, i've seen some that are pretty close, but they were scary and i'm not really sure if they were females or not), but we can handle most of what the business throws at us. I'm guessing you are about my build, so just hit the gym a little bit and i think you'd have very few problems.
unfortunately, there will be times when muscle is needed...i remember a car went down a 30 ft embankment and we made it down there, but there was no light and i needed to get to the truck. rescue took forever (so it seemed) and i was really upset with myself for not being able get him out and to the truck without calling for help. i honestly feel pt care suffered a bit (although he is alive and well today). BUT, on the other hand, i'm the smallest person around and can recall a few times when I was the only one who could make it to the pt.
so, after rambling, my point is that you will be fine. try your best and remember we all have strengths and waknesses. pt care is most important so make that your priority. no one wants a strong EMT that can lift them, but can't treat them.
good luck,
streetdoc