Congrats on your BFP!!
And boo to being ill!!
Yes it will feel tough going back to training after illness as you may feel like you have been hit by a truck. Add pg hormones now in your system (tired, hungry, hot, cold, relaxin starting) and you feel like you are swimming in the wrong direction.
My best advice is grab one of the personal trainers at your gym who has studied pre and post natal exercise for a quick 'tune up'. You may be surprised to find that as a seasoned exerciser that you can carry on with your programme but with a few tweaks: these may be to your exercises or to your diet or both. You may fancy a complete overhaul and try something specifically for pg. many ladies find they love the water at this time (maybe once bump is bigger?) as you will get a complete cardio and toning workout with less stress to joints and your working heartrate whilst others keep on with their classes (bodybalance/bodyflow is one good example) but take the 'lower intensity option' and the 'pg adaptation options' you can still get a great workout with these, its just choosing options to suit your circumstance. You can still train your abs and back to the end of the first tri, you can still lift and get your cardio fix but as with all new lifestyle changes please consult a professional before starting them.
Surprise yourself at what you are still able to do but listen to your body and don't be a hero. Keep with the fluids and if something feels wrong STOP!! also ask for some new post exercise muscle stretches as your ligaments (and tendons to a point) are starting to relax so you may end up over stretching.
Happy and Healthy 9months to you xxxx
EDIT: If you are taking or have taken any supplements for pre or post training PLEASE check on the label and with a GP if they are still suitable. Some protein powders contain caffeine etc, some exercise pills contain ingredients unsuitable for pg or bfing ladies.