Thanks for the query.
If you have vomitings that can lead to dehydration
which intern can lead to headache.
Take plenty of water, fruit juices etc which will help to some extent.
Some amount of tightening of abdomen is common during pregnancy
because of painless uterine contractions called Braxton Hicks contractions
If your pain increases gradually and any associated spotting etc develops better to consult your doctor and get examined.
Better to avoid or decrease the frequency of intercourse during the first three months.
Lateral position is preferable in intercourse during pregnancy.