Can I use lemsips while pregnant?

Probably no. Without knowing your gestational age (how far along) it's hard to say definitely. Paracetamol (aka tylenol) is safe as long as below toxic levels--best to keep below 2gm daily. The decongestant has not been fully tested in pregnancy--these ages constrict or narrow blood vessels so it would be best to avoid unless benefit outweighs risk. No cough/cold med has been shown to effectively shorten colds.